Fixed a bunch of clang -Wabsolute-value warnings

Various places used abs(), which takes int, when dealing with
floating point numbers.  Use fabs instead.

Change-Id: If6f2f3784f199a3a60dcf0d1e8e96bf5ee4deb92
Merge topic 'clang-Wabsolute-value' into master

f062ed5a Fixed a bunch of clang -Wabsolute-value warnings