Allow global vars without global modifier in explicit mode.

[neilsf]

To access a global variable, the global modifier \ is currently mandatory in functions and procedures. However, the #100 explicit mode coming in V3 should allow to refer to global variables without the modifier.

Example:

PRAGMA explicit_mode = 1

DIM someGlobalVar AS int

PROC myProc
  REM notice there's no backslash before the variable name
  PRINT someGlobalVar
ENDPROC