DexDeclareFile allows test producers to write test files with .dex extensions that
contain pure dexter commands.
.dex file commands do not need to be commented out like they do when written
inline within test source files.
DexDeclareFile commands are declarative in behaviour, they state that any Dexter
command seen from this point on will have its path attribute set to the path
declared in the DexDeclareFile command.
Provided in this patch is in the implementation of DexDeclareFile and 4 tests.