File in the contents of the receiver.
During a file in operation, global variables (starting with an
uppercase letter) that are not declared don't yield an `unknown
variable' error. Instead, they are defined as nil in the `Undeclared'
dictionary (a global variable residing in Smalltalk).
As soon as you add the variable to a namespace (for example by creating
a class) the Association will be removed from Undeclared and reused
in the namespace, so that the old references will automagically point
to the new value.
fileInLine: lineNum file: aFile at: charPosInt
Private - Much like a preprocessor #line directive; it is used internally
by #fileIn, and explicitly by the Emacs Smalltalk mode.