Update 43: Implemented some language changes.

GP 2 no longer has an injective flag in its rule declarations. These
have been removed from the lexer, parser and any appropriate
structures/functions. In addition, commas are no longer present
between nodes and edges in a graph.

seman.c
- Added extra semantic checking to forbid degree operators and length
  operators in LHS labels.
- Corrected semantic checking of degree operators as they can occur
  in a RHS label or in a condition. Previously the code assumed the
  latter case.
- Fixed an error in enter_variables: Upon reaching a CHAR_DECLARATIONS,
  the integer_count was incremented.

pretty.c
- Fixed a couple of bugs concerning the printing of rule nodes and the
  printing of bidirectional edges.