add chmodzip utility

I've been using this to set execute attribute bits when zipping release packages on windows, because the windows zip32 utility doesn't. Usage is like:

dmd2.zip:
        del dmd2.zip
        zip32 -r dmd2 \dmd2\*
        chmodzip dmd2.zip 0755 \
        dmd2/freebsd/bin32/rdmd \
        dmd2/freebsd/bin32/dmd \
        dmd2/freebsd/bin32/obj2asm \
        dmd2/freebsd/bin32/dumpobj \
        dmd2/freebsd/bin32/dman \
        dmd2/freebsd/bin32/shell \
        dmd2/freebsd/bin32/ddemangle \
        dmd2/linux/bin32/rdmd \
        dmd2/linux/bin32/dmd \
        dmd2/linux/bin32/obj2asm \
        dmd2/linux/bin32/dumpobj \
        dmd2/linux/bin32/dman \
        dmd2/linux/bin32/ddemangle \
        dmd2/linux/bin64/rdmd \
        dmd2/linux/bin64/dmd \
        dmd2/linux/bin64/obj2asm \
        dmd2/linux/bin64/dumpobj \
        dmd2/linux/bin64/dman \
        dmd2/linux/bin64/ddemangle \
        dmd2/osx/bin/dumpobj \
        dmd2/osx/bin/obj2asm \
        dmd2/osx/bin/shell \
        dmd2/osx/bin/dmd \
        dmd2/osx/bin/rdmd \
        dmd2/osx/bin/dman \
        dmd2/osx/bin/ddemangle