This is a working semi-deforked application.  i.e. most of it is still in the com.android.email namespace, but choice bits are in com.fsck.k9 so that it won't try to overwrite the builtin client.

Changes: corrected the package (or something equally simple for K9.java
build.xml has an additional stanza that copies the R.java file from fsck to android namespace, and changes the package inside the file.
AndroidManifest.xml has the package set to fsck, and all the activities are now explicity named.