Swap out booleans in ancestors map with ints

This converts the myriad of `!0`s in the optimized code with `1`s, saving about 4kb on `reversi.js`. `ancestors` is only every used in `ClassTypeData`, and there its usages are wrapped in `!!()` so the fact that it's an int instead of a boolean is immaterial.
updated corejslib to use 1 instead of true for ancestor maps
Added java_lang_Object to its own ancestor hash
Added option 'relativeSourceMaps' to sbt plugin
Merge pull request #148 from Peluko/relative-source-maps

Added option 'relativeSourceMaps' to sbt plugin
Merge pull request #145 from lihaoyi/patch-1

Swap out booleans in ancestors map with ints