Enable interactive error reporting in a more standard manner

[GillesDuvert]

During interactive input one must see this:

GDL> n[z,]=3
     ^
% Syntax error.

or the same error in a procedure / include ('@')

GDL> test_const

n[1,] = 1
     ^
% Syntax error.
  At: /XXXX/YYYY/const.pro, Line 2
No parser output generated.
% Procedure not found: TEST_CONST
% Execution halted at: $MAIN$          
GDL> 

This is more or less what this patch does.

• closes no lineno info in error mesgs using @ (also wrong filename in error message) #59
• closes Remove dangerous code in ANTLR gdlc.g #1805
• add a few liberty to 'implied print". one can now type

GDL> a="a string"
GDL> a,dist(3), cos(!dpi)
a string
       0.0000000       1.0000000       1.0000000
       1.0000000       1.4142135       1.4142135
       1.0000000       1.4142135       1.4142135
      -1.0000000000000000

not necessary super useful but works with IDL.
but

GDL> !x.tickv
% AutoPrint currently impossible on structure/objects elements.

because ANTLR2 delivers the expression to a too-specialized routine and breaking this is utterly dangerous.

In summary, waiting for ANTLR4, "implied print" handling (not expressed in the ANTLR2 syntax but treated at try{}catch() level) make things more complicated than necessary.