pgsql: Reimplement pgbison and pgflex as perl scripts instead of bat fi

Reimplement pgbison and pgflex as perl scripts instead of bat files.

In the process, remove almost all knowledge of individual .y and .l files,
and instead get invocation settings from the relevant make files.
The exception is plpgsql's gram.y, which has a target with a different
name. It is hoped that this will make the scripts more future-proof,
so that they won't require adjustment every time we add a new .l or .y
file.

The logic is also notably less tortured than that forced on us
by the idiosyncrasies of the Windows command processor.

The .bat files are kept as thin wrappers for the perl scripts.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/c895e775a57072b075b230d60381ac432520b1a8

Modified Files
--------------
src/tools/msvc/pgbison.bat | 54 +++----------------------------
src/tools/msvc/pgbison.pl | 48 +++++++++++++++++++++++++++
src/tools/msvc/pgflex.bat | 48 +++-------------------------
src/tools/msvc/pgflex.pl | 76 ++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 134 insertions(+), 92 deletions(-)