A dash character is illegal in function names in sh (but not bash). Since
our shell tasks run under sh and the shell parser is sh based, EXPORT_FUNCTIONS
won't work with class names containing a dash.
We can't change sh, we can ensure the user is warned about the problem
straight away though.
[YOCTO #7006]
(Bitbake rev: 86704281b79e524dccccc88cbf996b299b33bae2)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>