Fix bug in local_abs_merge optimization
Better error message if the length of the shape cannot be determined.
Merge pull request #1340 from lamblin/reshape_better_msg

Better error message if the length of the shape cannot be determined.
Do not attempt compilation without a compiler

This fixes a crash on "import theano" when g++ is not available.
Merge pull request #1339 from lamblin/fix_merge_abs

Fix bug in local_abs_merge optimization
Merge pull request #1342 from delallea/minor

Do not attempt compilation without a compiler