Signed off contributors

Added in BSD license to files

Partially fixed qualifying the empty set constant with its type
Merge branch 'devel-smt' of github.com:Whiley/WhileyCompiler into devel-smt
Changed copyright author
WyC: minor updates ahead of next release.
Merge pull request #413 from hjwylde/devel-smt

Pulling your changes.  Sorry they didn't make the latest release, but they'll be in v0.3.29, to be released next week!
Merge remote-tracking branch 'origin/devel-smt'

Conflicts:
	modules/wycs/src/wycs/solver/smt/Solver.java
	modules/wycs/src/wycs/solver/smt/Sort.java
	modules/wycs/src/wycs/transforms/SmtVerificationCheck.java
WyIL: Added enable flag for BackPropagation #416.
The BackPropagation phase did not have an enable flag, which seems
unsusual compared with other WyIL transforms.  Therefore, I've added
one!
Updated .gitignore to include smt2 files.
The smt2 files are generated by the SmtVerificationCheck phase, and
are only temporary files.
Merge branch 'master' into devel-assert

Conflicts:
	modules/wyc/src/wyc/builder/FlowTypeChecker.java