More fixes for libpq's .gitignore file.

The previous patches failed to cover a lot of symlinks that are only
added in platform-specific cases.  Make the lists match what's in the
Makefile for each branch.

src/interfaces/libpq/.gitignore

-/encnames.c
 /exports.list
-/ip.c
-/md5.c
+/crypt.c
+/getaddrinfo.c
+/inet_aton.c
 /noblock.c
+/open.c
 /pgstrcasecmp.c
+/snprintf.c
+/strerror.c
 /strlcpy.c
 /thread.c
+/win32error.c
+/pgsleep.c
+/md5.c
+/ip.c
+/encnames.c
 /wchar.c