Provider using package service is expected to use 'exec' instead of 'cmd'

[LaurentTreguier]

According to the documentation, the command for a build is supposed to be in the cmd key. However, when looking at the code, the cmd key is not used and the (apparently undocumented) exec key is used instead.

This can be seen in build-make. Is there a problem in the docs, or is the key really supposed to be different ? (and if it is so, why ?)