Update Location.convert() javadocs to reflect their inconsistency with locales.

The Location.convert() methods do not invert each other as might be
expected. Changing this would introduce breaking changes, so I've
updated the javadocs to make this clearer.

Bug: 13280976
Change-Id: If4bd3c83d5fb67915450849ca471aabc27544dac
1 file changed