Set the network variable via enviroment variable (closes #3488)

If the environment variable 'DMAKE_NETWORK' is set, use it instead of
guessing the network. Fixes problems with FN network.
Corrected oversampling logic bug
(closes #3425)
Added support for second-order lagrange elements
(refs #3425)
Avoid creating/destroying vector.  Ref #3494.
MechFunctions only re-built if mesh adapts; added tests that mimic ex02
(refs #3425)
Merge pull request #3489 from andrsd/dmake-fn-network-fix

Set the network variable via enviroment variable (closes #3488)
Merge pull request #3497 from jasondhales/bilinear_3494

Avoid creating/destroying vector.  Ref #3494.
Merge pull request #3498 from aeslaughter/oversample-3425

Corrected oversampling seg. fault