Make the results of IvyResolve be target-dependent.
Make the results of IvyResolve be target-dependent.

Previously the classpath file was always the latest one computed, even
if you then start working on a different target whose BUILD files
haven't change (and therefore won't trigger a new resolve).

This change qualifies each classpath file with (a hash of the ids of)
the targets it was generated from, and the main classpath file is now
a symlink to the appropriate one.

Signed-off-by: John Sirois <82d8b9acb65478c2cf98f3a8c11b3322c3423201@twitter.com>

ericzundel/commons,nkhuyu/commons,brutkin/commons,nkhuyu/commons,foursquare/commons-old,foursquare/commons-old,cevaris/commons,atollena/commons,jsirois/commons,foursquare/commons-old,Yasumoto/commons,Yasumoto/commons,brutkin/commons,atollena/commons,WCCCEDU/twitter-commons,pombredanne/commons,jsirois/commons,Yasumoto/commons,cevaris/commons,imsut/commons,cevaris/commons,pombredanne/commons,ericzundel/commons,VaybhavSharma/commons,VaybhavSharma/commons,ericzundel/commons,nkhuyu/commons,VaybhavSharma/commons,pombredanne/commons,nkhuyu/commons,VaybhavSharma/commons,Yasumoto/commons,ericzundel/commons,atollena/commons,brutkin/commons,Yasumoto/commons,WCCCEDU/twitter-commons,pombredanne/commons,WCCCEDU/twitter-commons,brutkin/commons,abel-von/commons,imsut/commons,cevaris/commons,jsirois/commons,abel-von/commons,jsirois/commons,atollena/commons,ericzundel/commons,abel-von/commons,VaybhavSharma/commons,jsirois/commons,abel-von/commons,atollena/commons,imsut/commons,WCCCEDU/twitter-commons,abel-von/commons,nkhuyu/commons,brutkin/commons,cevaris/commons,pombredanne/commons,WCCCEDU/twitter-commons