26d723e0 broke this, but I have no idea how it ever worked *after* that
change (it probably didn't). The problem is that untarring checks for
"malicious" tarfiles and in the process, normalizes entry paths. If the
outer path is not normalized, the subpath check fails.

Removed StringEscape
Removed z3 and other windows executables from the git index.

Fix semantics for substring
Simpler values for enumeration, externalised special values to disambiguation.
Removed the previous reference to leon.lang.string
Removed unused and redundant code.

Conflicts:
	src/main/scala/leon/xlang/ImperativeCodeElimination.scala

Improve equality to detect equalities between literals

- InputSplit splits by a boolean input variable

- IndependentSplit splits output variables that are unrelated

Added Either in Leon Library. Fixed some code gen issues in Windows.