Make it possible to create erlydtl beam files with full path in the name

if DTL_FULL_PATH=true
  /templates/a/b/c.dtl -> a_b_c_dtl.beam
otherwise (as it was before)
  -> c_dtl.beam

With this change it will be possible to create templates with the same name in different directories.
You can put it on the previous line, no point wasting space.