win codepages 1253, 1254, 1255, 1257 and cleanup

The attached patch adds support for windows codepages 1253, 1254, 1255,
and 1257 and cleans up a bunch of the support utilities.

1) In src/backend/utils/mb/Unicode remove nearly duplicate copies of the
UCS_to_XXX perl script and replace with one version to handle all generic
files.  Update the Makefile so that it knows about all the map files.
This produces a slight difference in some of the map files, using a
uniform naming convention and not mapping the null character.

2) In src/backend/utils/mb/conversion_procs create a master utf8<->win
codepage function like the iso-8859 versions instead of having a separate
handler for each conversion.

3) There is an externally visible change in the name of the win1258 to
utf8 conversion.  According to the documentation notes, it was named
incorrectly and I've changed it to a standard name.
http://www.postgresql.org/docs/8.1/static/functions-string.html#FTN.AEN7664

Running the unicode mapping perl scripts has shown some additional mapping
changes.  I've attached these separately.  The changes to koi8r and
iso8859-7 look correct to me after checking a few changes against some
code charts, but the euc_jp and sjis changes remove a number of mappings.
I don't know anything about them and wouldn't suggest applying them, but
wanted to pass them along.

Kris Jurka