Incremental pretty-printing

Merged modifications in QuestionBuilder
Better imports in StringRender.scala

# Conflicts:
#	src/main/scala/leon/synthesis/ExamplesFinder.scala
#	src/main/scala/leon/synthesis/disambiguation/ExamplesAdder.scala
#	src/main/scala/leon/synthesis/disambiguation/QuestionBuilder.scala
#	src/main/scala/leon/synthesis/rules/StringRender.scala

Strings for smt-Z3

Corrected a Lambda expression conversion bug

Ensures that no conversion occurs if only fundefs in the library use strings.
Forward and backward conversion for embedded evaluators in FairZ3

Convert IDs only if the type change.

# Conflicts:
#	src/main/scala/leon/purescala/ExprOps.scala

# Conflicts:
#	src/main/scala/leon/purescala/DefOps.scala
#	src/main/scala/leon/solvers/z3/AbstractZ3Solver.scala

Two-step function body replacement to take into account all function changes.
Bijection adds new methods.