Van der Waals gas density added.  Fixes #3244 .  Doco and test included
remove from valid params (#3341)
Merge pull request #3348 from dschwen/split_3341

Remove 'c' from valid params
Merge commit '0db91e1b810e211ece4e185a2702702886563c2b'
Remove "c" from failing test - refs #3341
Merge pull request #3330 from WilkAndy/methane_3244

Van der Waals gas density added.  Fixes #3244 .  Doco and test included
Merge commit '617654789fdc8d4a68f14932b8f7374afc6a86e0'
Merge commit 'ae8dc9d59bf5f0248f02cf0692267d2c41b8ff3f'