pgsql: ECPG requires a local include directory to override the

Log Message:
-----------
ECPG requires a local include directory to override the project-wide ones.
Add ability to add "prefix include directories", and use it...

With this, ecpg regression tests now pass on MSVC builds.

Modified Files:
--------------
    pgsql/src/tools/msvc:
        Mkvcbuild.pm (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Mkvcbuild.pm.diff?r1=1.12&r2=1.13)
        Project.pm (r1.11 -> r1.12)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/msvc/Project.pm.diff?r1=1.11&r2=1.12)