[e-acsl] improve test of function contract

- Fixed Makefile's bug

[e-acsl] fix unexpected interaction with Frama-C compilation when compiling it with --enable-external

[e-acsl] generate nice variable names whenever possible

	 - fixed bug when reusing variables in a different typing context
	 - fixed bug with boolean
	 - fixed bug with negation and GMP integers
	 - fixed bug with conditional and GMP integers
	 - fixed wrongly generated oracles

[e-acsl] bug fixed in functions with both a postcondition and multiple returns

* fixes bug:
  - fixed bug in quantifications when the bound variable got C type
  - fixed bug with DEV_FLAGS in Makefile.in
* implements new E-ACSL features:
  - invariant as assertion
  - existential quantification \exists over integers
  - equivalence <==>
  - \at as a predicate
  - conditional _ ? _ : _ (for terms and predicates)
  - binary boolean operations over terms
  - mixed assumes and ensures in function contracts
* other new features:
  - better error messages when runtime checks fail 
    (replace e_acsl_fail by e_acsl_assert)
  - remove option -e-acsl-assert
  - add E-ACSL manuals in doc/manuals
  - add files doc/Changelog, INSTALL, README and VERSION
  - new option -e-acsl-version
  - check Frama-C version at configure
  - make src-distrib
  - header 2012

[e-acsl] universal quantifications done (including testing)