Fix #2, cannot include path on Save()

Save() function does not accept full path. Bug only happens when drag
and drop because that is when the full path is given (normally we would
only give the source file name as the argument). Therefore, only the
filename is given in the fixed code, while the output directory is
specified in DefineDynamicAssembly() when output directory is not where
the compiler is running.
Merge pull request #3 from yamgent/bug-dragdropsource

Fix #2, cannot include path on Save()