New backend directory description file.

src/BACKEND_MAP

+access          various index access methods
+access/common           common access routines
+access/gist             easy-to-define access method system
+access/hash             hash
+access/heap             heap
+access/index            index handling
+access/nbtree           btree
+access/rtree            rtree
+access/transam          transaction manager (BEGIN/ABORT/COMMIT)
+bootstrap       handles initdb requests to create initial template database
+catalog         system catalog manipulation
+commands        commands that do not require executor
+executor        executes complex node plans from optimizer
+include         include files
+lib             support library
+libpq           communication to client libpq library routines
+main            passes control to postmaster or postgres
+nodes           creation/manipulation of nodes
+obj             object files
+optimizer       creates path and plan
+optimizer/path          creates path from parser output
+optimizer/plan          optmizes path output
+optimizer/prep          handle special plan cases
+optimizer/util          optimizer support routines
+parser          converts SQL query to query tree
+postmaster      controls postgres server startup/termination
+regex           regular expression library
+rewrite         rules system
+storage         manages various storage systems
+storage/buffer          shared buffer pool manager
+storage/file            file manager
+storage/ipc             semaphores and shared memory
+storage/large_object    large objects
+storage/lmgr            lock manager
+storage/page            page manager
+storage/smgr            storage(disk) manager
+tcop            traffic cop, dispatches request to proper module
+tioga           array handling?
+utils           support routines
+utils/adt               built-in data type routines
+utils/cache             system/relation/function cache routines
+utils/error             error reporting routines
+utils/fmgr              function manager
+utils/hash              hash routines for internal algorithms
+utils/init              initialization stuff
+utils/mmgr              memory manager(process-local memory)
+utils/sort              sort routines for internal algorithms
+utils/time              transaction time qualification routines
+
+port            port-specific files
+port/BSD44_derived
+port/aix
+port/alpha
+port/bsdi
+port/bsdi_2_1
+port/dgux
+port/hpux
+port/i386_solaris
+port/irix5
+port/linux
+port/sparc
+port/sparc_solaris
+port/svr4
+port/ultrix4
+port/win32
+port/win32/regex
+port/win32/sys