Work better with mainline gdb (#192)

* Parse floats the way mainline gdb prints them.

For 64-bit floats, it shows both float and double results. Now more
tests pass using mainline gdb.

* Disable ANSI when talking to gdb.

Helps more tests pass with mainline gdb.

* Parse {float=...,double=...} in "info registers"

Makes tests work better with mainline gdb.