Pike compiler mega patch.

Added predef::CompilerEnvironment, which is a wrapper for struct compilation.
Moved the definition of struct compilation to the new header file "pike_compiler.h".
The compilation struct is now contained in the current context in the current_object during compilation.
The global variable lex is no more, it has moved into the compilation struct.
Added enter_compiler() and exit_compiler().
predef::compile() is now shorthand for predef::CompilerContext()->compile().

Rev: src/builtin_functions.c:1.652
Rev: src/compilation.h:1.35
Rev: src/docode.c:1.197
Rev: src/docode.h:1.20
Rev: src/dynamic_load.c:1.90
Rev: src/encode.c:1.263
Rev: src/language.yacc:1.411
Rev: src/las.c:1.406
Rev: src/lex.c:1.121
Rev: src/lex.h:1.36
Rev: src/lexer.h:1.66
Rev: src/module.c:1.52
Rev: src/object.c:1.284
Rev: src/operators.c:1.230
Rev: src/pike_compiler.h:1.1
Rev: src/pike_types.c:1.321
Rev: src/program.c:1.660
Rev: src/program.h:1.237