Allow for rebuilding a single component package

It is pretty common when developing code and using anvil to install and setup that code that you want to be able to easily rebuild the package that has the changed code in it so that it can be installed and tested. It might be nice if we can add a 'rebuild' package command line option (?) that will do just this. Or provide instructions on how users of anvil can avoid the package building process (for the component they are working on) by linking in there code via setup.py --develop instead of via a rpm build process.