Workaround for compiler warning.

Sadly, the previous code was correct and might even have been
infintesimally faster.  There's definitely never going to be an
uninitialized variable use here, but I can see no better way to
convince any non-AI compiler of that fact, and I fear if we don't
maintain libMesh to compile warning-free then I'll eventually start
ignoring *real* warnings too.
Fix for older app Makefiles

Makefiles based on our old examples typically pulled in object pattern
rules from Make.common but then used libmesh_CXX as the linker.  That
broke when we switched the obj-suffix to specify libtool rather than
raw object files.  This fixes it, still remains compatible with new
"fixed" app Makefiles which use libtool as the linker, and allows
newer Makefiles to easily choose one or the other method.
Updating statistics for April 2013.
Updating Millett 2013 reference.
Adding Kirk 2013 reference.
Added Swiler 2013 reference.
DofMap can report if it is capable of using blocked storage
support for --enable-blocked-storage
PETSc BAIJ support
trivial formatting
extend blocksize option to matrices init()ed without the help of the DofMap
towards add_block_matrix()
Check version for petsc-dev
Fix in config comment
Add macros for thread-local storage
petsc-3.4: VecType, PCType, and KSPType are now const typedefs
Merge pull request #102 from jedbrown/jed/petsc-3.4

petsc-3.4 support
Added Widmer 2013 reference.
Updated Bhalla 2013 preprint.
Updated Bittl preprint.