[petsc-dev] added crude parallel palltests for quicker alltests

[Barry Smith]

  I've added a crude new make rule palltests that runs multiple tests in different directories at the same time and gathers all results (at the end) into alltests.log in branches master and next. It reduced a basic debug alltests on my laptop from 25 minutes to 7 1/2 minutes. 

  Now less excuse for not running some full testing before merging to next.

  Barry