Add support for Windows codepages 1253, 1254, 1255, and 1257 and clean

up a bunch of the support utilities.

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.

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.

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 this changes it to a standard name.

Running the Unicode mapping perl scripts has shown some additional mapping
changes in koi8r and iso8859-7.