Remove an incorrect assert.

The assert was added conservatively when copy/pasting code, but there
is no reason that an Inactive live range should overlap (or not
overlap) with the current live range under consideration.
Fix a bug in compare/branch fusing.  Refs #28.

The pattern-matching code was assuming that a branch instruction
following the icmp instruction is a conditional branch and then
testing its source operand.  If the branch instruction happens to be
unconditional, then there is no source operand to test, and no
opportunity for compare/branch fusing.
"make format" change.