PostgreSQL 6.4 patches - portability related.

The attached patches affect the following areas:

1. The make file for 'bin/pgtclsh' was failing on my system because the tcl/tk
libraries could not be found. I have changed the make file so that it uses
the contents of tclConfig.sh and tkConfig.sh to obtain the information it
needs to link the programs.

Affected files (relative to the PGSQL source directory):

src/configure, src/configure.in, src/bin/pgtclsh/Makefile

New files (relative to the PGSQL source directory):

src/bin/pgtclsh/mkMakefile.tcltkdefs.sh.in

2. On my system, '/usr/lib' contains the information for tcl7.6 and tk4.2,
which is used for the SCO System Administration tool. '/opt/lib' contains
the information tcl8.0 and tk8.0, which I used for my development purposes.
Configure was finding the wrong one even if I used '--with-libs=/opt/lib'
to specifiy the directory to use. This patch corrects this by changing the
order in which directories are searched for the [tcl|tk]Config.sh files so
that '/usr/lib' is searched last. This change is in keeping with the help
message that states that '--with-libs' is used to specify the site library
directories for TCL/TK, etc.

Affected files (relative to the PGSQL source directory):

src/configure, src/configure.in

3. The file that creates the 'Makefile.tcldefs' file in 'pl/tcl' left unex-
panded variable references the created file. For example:

TCL_LIB_FILE = libtcl8.0${TCL_DBGX}.so

This patch corrects the problem.

4. The installation of 'libpgtcl.so' was failing because 'libpgtcl.so' already
existed as a symbolic link to a file. This patch corrects the problem by
explicitly removing libpgtcl.so from the destination directory.

Affected files (relative to the PGSQL source directory):

src/interfaces/libpgtcl/Makefile.in

With these changes, the only manual changes I make after running configure is
to add '-o' and '-g' options to the INST_EXE_OPTS, INSTL_LIB_OPTS, and
INSTL_SHLIB_OPTS variables in 'Makefile.global'. I do this so that the correct
owner and group are assigned when I install postgreSQL (as root).