wxwidgets: keeping in-source build (resolves #299)

This commit provides the autotools-brokensep class and uses it for
the wxwidgets recipe.
The autotools-brokensep indicates that this package currently cannot
handle out-of-source builds, and hence the in-source build must be
kept until this is resolved.
The autotools-brokensep class is a copy of the autotools-brokensep
class provided in the openembedded-core commit 006b8a78 [1].
To make this commit backwards compatible to even earlier versions
of openembedded-core, we provide this class in meta-ros ourselves.

[1] http://cgit.openembedded.org/openembedded-core/commit/?id=006b8a7808a58713af16c326dc37d07765334b12
Merge pull request #300 from KristofRobot/wxwidgets

wxwidgets: keeping in-source build (resolves #299)