Merge pull request #351 from linas/master

Simplify how AttentionValue is used.
Merge pull request #353 from linas/master

remove a lot of un-needed or duplicate code
Fix ubigrapher build breaks
ubigrapher: missed a spot
ubigraph: more bug fixes

I'm coding blind, here...
ubigrapher: one more bug
fix compiler warning
Export the AV changed signal
Atomspace: Change signature of the merge signal.

Also, the OAC was asking for and getting the wrong signal ...
atomspace: fix bad indentation
oops, typo in previous commit
bugfix: decaySTI was not issueing a signal.
UTests: change to the new signal signature
atomspace: define a type signal.