Semi-pruned SSA support for sea-ir.

Added the following:

Per file:
sea_ir/sea.*: IDominator pass, dominance frontiers, global variables for ssa
              transformation, phi-function insertion pass, SSA renaming pass.
sea_ir/instruction_tools.*: These tools provide info needed by dataflow analysis
                            that is dependent on dex format.
compiler/utils/scoped_hashtable.h: Scoped hashtable implementation that
                                   allows fast SSA renaming.
src/compiler/utils/scoped_hashtable_test.cc: Test for scoped_hashtable.h.
dex_instruction.cc: Changed semantics of the VRegA,B,C function
                    to return NO_REGISTER instead
                    of aborting if the instruction does not
                    have register operands.
Android.common.mk: Added support for scoped_hashtable test.

Change-Id: I990fe4c213d241a033e43a04a67c6083fca4b347