bash_it.sh: Patched changes made to support custom.*.bash files.

Code was added to support loading
custom.{aliases,completion,plugins}.bash from their respective
directories in 46f6701a3. The change made in that commit does not wait
until the enabled {aliases,completion,plugins}/*.bash files are loaded
before sourcing the custom.*.bash files, which was the case before. This
patch fixes any issues caused by that change by loading the enabled
*.bash files and custom *.bash files in two successive for loops.