pgsql: When using MSVC, disable the building of ecpg if pthreads is not

Log Message:
-----------
When using MSVC, disable the building of ecpg if pthreads is not
specified.

Magnus Hagander

Modified Files:
--------------
    pgsql/src/tools/msvc:
        Project.pm (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Project.pm.diff?r1=1.6&r2=1.7)
        Solution.pm (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Solution.pm.diff?r1=1.7&r2=1.8)
        mkvcbuild.pl (r1.10 -> r1.11)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/mkvcbuild.pl.diff?r1=1.10&r2=1.11)