Compare Safari build numbers by parts instead of floats

This changes the way the Safari build numbers are compared to compare
each part instead of trying to convert it to a float to compare. This
prevents warnings for three-part build numbers and allows three-part
build numbers to be added to the lookup list in the future.
Merge pull request #62 from dougwilson/fix/safari-build-cmp-warning

Compare Safari build numbers by parts instead of floats