Ensure that distributed timezone abbreviation files are plain ASCII.

We had two occurrences of "Mitteleuropäische Zeit" in Europe.txt,
though the corresponding entries in Default were spelled
"Mitteleuropaeische Zeit".  Standardize on the latter spelling to
avoid questions of which encoding to use.

While here, correct a couple of other trivial inconsistencies between
the Default file and the supposedly-matching entries in the *.txt
files, as exposed by some checking with comm(1).  Also, add BDST to
the Europe.txt file; it previously was only listed in Default.
None of this has any direct functional effect.

Per complaint from Christoph Berg.  As usual for timezone data patches,
apply to all branches.

Discussion: https://postgr.es/m/20200716100743.GE3534683@msg.df7cb.de

src/timezone/tznames/Antarctica.txt

@@ -13,7 +13,7 @@ AWST    28800    # Australian Western Standard Time
 CLST   -10800 D  # Chile Summer Time (obsolete)
 CLT    America/Santiago  # Chile Time (obsolete)
 DAVT    Antarctica/Davis  # Davis Time (Antarctica) (obsolete)
-DDUT    36000    # Dumont-d`Urville Time (Antarctica) (obsolete)
+DDUT    36000    # Dumont-d'Urville Time (Antarctica) (obsolete)
 MAWT    Antarctica/Mawson  # Mawson Time (Antarctica) (obsolete)
 MIST    39600    # Macquarie Island Time (obsolete)
 NZDT    46800 D  # New Zealand Daylight Time

src/timezone/tznames/Australia.txt

@@ -7,7 +7,7 @@
 # src/timezone/tznames/Australia.txt
 #
 
-ACSST   37800 D  # Central Australia (not in IANA database)
+ACSST   37800 D  # Australian Central Summer Standard Time (not in IANA database)
 ACDT    37800 D  # Australian Central Daylight Time
                  #     (Australia/Adelaide)
                  #     (Australia/Broken_Hill)
@@ -17,7 +17,7 @@ ACST    34200    # Australian Central Standard Time
                  #     (Australia/Broken_Hill)
                  #     (Australia/Darwin)
 ACWST   31500    # Australian Central Western Standard Time (obsolete)
-AESST   39600 D  # Australia Eastern Summer Standard Time (not in IANA database)
+AESST   39600 D  # Australian Eastern Summer Standard Time (not in IANA database)
 AEDT    39600 D  # Australian Eastern Daylight Time
                  #     (Australia/Brisbane)
                  #     (Australia/Currie)

src/timezone/tznames/Default

@@ -597,8 +597,8 @@ CHUT    36000    # Chuuk Time (obsolete)
 CKT     Pacific/Rarotonga  # Cook Islands Time (obsolete)
 EASST   Pacific/Easter  # Easter Island Summer Time (obsolete)
 EAST    Pacific/Easter  # Easter Island Time (Chile) (obsolete)
-FJST    46800 D  # Fiji Summer Time (obsolete)
-FJT     43200    # Fiji Time (obsolete)
+FJST    46800 D  # Fiji Summer Time (caution: this used to mean -46800) (obsolete)
+FJT     43200    # Fiji Time (caution: this used to mean -43200) (obsolete)
 GALT   -21600    # Galapagos Time (obsolete)
 GAMT   -32400    # Gambier Time (obsolete)
 GILT    43200    # Gilbert Islands Time (obsolete)

src/timezone/tznames/Europe.txt

@@ -12,6 +12,7 @@
 #  - BST: Bougainville Standard Time (Papua New Guinea)
 BST      3600 D  # British Summer Time
                  #     (Europe/London)
+BDST     7200 D  # British Double Summer Time
 CEST     7200 D  # Central Europe Summer Time
                  #     (Africa/Ceuta)
                  #     (Europe/Amsterdam)
@@ -184,12 +185,12 @@ IST      3600    # Irish Standard Time
                  #     (Europe/Dublin)
 MEST     7200 D  # Middle Europe Summer Time
                  #     (MET)
-MESZ     7200 D  # Mitteleuropische Sommerzeit (German)
+MESZ     7200 D  # Mitteleuropaeische Sommerzeit (German)
                  #     (attested in IANA comments though not their code)
 MET      3600    # Middle Europe Time
                  #     (MET)
 METDST   7200 D  # Middle Europe Summer Time (not in IANA database)
-MEZ      3600    # Mitteleuropische Zeit (German)
+MEZ      3600    # Mitteleuropaeische Zeit (German)
                  #     (attested in IANA comments though not their code)
 MSD     14400 D  # Moscow Daylight Time (obsolete)
 MSK     Europe/Moscow  # Moscow Time