build.gant: use ${eclim.plugins} for `ln -s` commands

I have setup eclim.plugins to use the dropins/ directory instead, and
therefore the creation of the symlinks failed.
create relative symlinks when possible

refs #196
clean up unix deploy a bit

- remove windows bat,cmd,exe files from the eclim bin dir
- remove *.sed exclude to chmod since eclim no longer uses sed files
- suppress error output when attempting to remove symlinks when they
  don't exist.
update sphinx extensions to work w/ python3
more python3 sphinx compatability
add setting to globally toggle validate on write

refs #199
add setting to use omnifunc instead of completefunc

fixes #151
add Ctrl+X to list of keys to be disabled on vimplugin focus
don't load xml syntax mods if ft is cs

fixes #201
add support for junit jvmargs, syssprops, + envvars
update sdt support for Scala IDE 3.0.0

- fix commands for changes to the scala ide apis
- update the installer to support features w/ no update site since the
  scala ide has different plugin versions/updates sites depending on the
  eclipse/scala version combo the user is using.