Recognize both Big and Small representations of IntInfs.
Translate IntInf consts to Big and Small representations.

Translate IntInf consts to Big and Small representations in conversion
from SSA to RSSA.  This is consistent with the treatment of other
IntInf operations in the conversion from SSA to RSSA: the
IntInf_toVector, IntInf_toWord, Word_toIntInf, and WordVector_toIntInf
primitives are translated to simple casts and other IntInf_*
primitives are translated to C calls.  Hence, after the conversion
from SSA to RSSA, IntInf is no longer treated as a primitive.
Remove initIntInfs from program initialization.

Translating IntInf consts to Big and Small representations in
conversion from SSA to RSSA removes the need to initialize IntInf
constants from strings in runtime initialization.
Cosmetic formatting improvements.
Constant fold IntInf_toVector and WordVector_toIntInf primitives.
More efficient translation of IntInf const to Big representation.
Merge branch 'master' of https://github.com/MLton/mlton into int-inf-consts
Merge pull request #81 from MatthewFluet/int-inf-consts

IntInf constants updates.

Various updates to treatment of IntInf constants in the compiler. Highlights:
 * Recognize both Big and Small representations of IntInfs.
 * Translate IntInf consts to Big and Small representations in
   conversion from SSA to RSSA. This is consistent with the
   treatment of other IntInf operations in the conversion. After
   the conversion, IntInf is no longer treated as a primitive.
 * Remove initIntInfs from program initialization.
 * Constant fold IntInf_toVector and WordVector_toIntInf
   primitives.