Revise Tcl/Tk configuration. Make missing Tcl after --with-tcl an error,

Revise Tcl/Tk configuration.  Make missing Tcl after --with-tcl an error,
add --without-tk option to disable Tk.  We don't need the AC_PATH_XTRA
test because tkConfig.sh already contains all the information about how to
compile and link with X.  Also make sure that libpq is up to date for
libpgtcl.  Remove executable bits from pgaccess.sh, but add it to pgaccess.