experimental Watcom support

With the attached patch, I was able to build a non-debug Unicode psqlodbc
DLL with Open Watcom 1.2 on Windows 2000. I haven't actually tested it,
yet. This patch is probably not suitable for CVS. Use at your own risk.

I had to make one change to SQLSetDescField() in sqlucode.h, as described
in MinGW bug 890559 (Open Watcom apparently borrows MinGW's headers).

I encountered what appears to be a bug in Watcom's nmake clone. It
sometimes skips compiling a file. If you compile it by hand, then rerun
make, it works.

The following is a brief summary of the changes:

I added psqlodbc.rc to EXTRA_DIST in Makefile.am.

I added an _atoi64() work-alike to convert.c, because Watcom defines
ODBCINT64, but doesn't have _atoi64() or strtoll().

I changed an SQLColAttributeW() parameter from SQLINTEGER * to SQLPOINTER.

I removed a newline in psqlodbc.rc that Watcom's rc clone couldn't handle.

I commented out SQLSetScrollOptions from the .def file.

I aliased some of the functions in the .def file. This works around what
may be a misconfiguration in the linker. I was getting warnings like

Cannot extract external symbols ... fuzzy linking may not work

I removed some quotes in the Makefile that Watcom's cl clone couldn't handle.