pgsql: Fix some corner-case bugs in _sendSQLLine's parsing of SQL

Log Message:
-----------
Fix some corner-case bugs in _sendSQLLine's parsing of SQL commands
> found in a pg_dump archive.  It had problems with dollar-quote tags
broken across bufferload boundaries (this may explain bug report from
Rod Taylor), also with dollar-quote literals of the form $a$a$...,
and was also confused about the rules for backslash in double quoted
identifiers (ie, they're not special).  Also put in placeholder support
for E'...' literals --- this will need more work later.

Modified Files:
--------------
    pgsql/src/bin/pg_dump:
        pg_backup_archiver.h (r1.66 -> r1.67)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_archiver.h.diff?r1=1.66&r2=1.67)
        pg_backup_db.c (r1.64 -> r1.65)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_db.c.diff?r1=1.64&r2=1.65)