Change buildcustom behavior

instead of building a custom artifact for every patch/$custom directory,
specify the directory and apply the patches after the general patches
have been applied. Allows building of aSmack 4.0 with

./build.bash -b 4.0 -c 4.0

Also rename 40-enable-custom-sasl.sh to 30-enable-custom-sasl.sh just
for the directory listing.