Allow TimeSolver tolerances relative to first step

Specifying a negative tolerance now lets you avoid trying to directly
calculate or guess what a decent L2/H1/whatever error growth rate is,
by using a multiple of the growth rate observed at the initial time
step.
Better AdaptiveTimeSolver documentation
Merge pull request #184 from libMesh/time_solver_tolerance

Allow TimeSolver tolerances relative to first step
Merge pull request #186 from aeslaughter/exodus2

Allow ExodusII_IO to have empty variable list
Adding Perez, 2013b.
Updating statistics for December 2013.
Adding code to detect the value of PETSC_VERSION_RELEASE during
configure.
Ran bootstrap.
Adding PETSC_RELEASE_LESS_THAN macro.
Using new PETSC_RELEASE_LESS_THAN macro.
Merge branch 'petsc_release'
Upcoming petsc-3.5 API changes.
Use terser PETSC_RELEASE_LESS_THAN macro.
Merge branch 'dmitry_3.5'
Fall back to the old PETSC_VERSION_LESS_THAN macro for old PETScs.
Fix overzealous assert

Our assertion wasn't compatible with our workaround for a METIS bug;
this gets exposed when partitioning a completely disconnected mesh.
Added build scripts from Derek
Added a python build script