[Ada] fix handling of very long lines in scanner

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

This patch corrects the handling of programs containing very long source
lines which after tab expansion have more than 32766 characters. Such lines
cause various problems given that the column number types are only 16 bits.
This patch diagnoses such bizarre lines cleanly and abandons compilation.

The following is a test program

procedure truc is
begin
  <4096 horizontal tab characters> null;
end;

This now gives a clean error:

truc.adb:3:01: this line is longer than 32766 characters
compilation abandoned

2007-06-06  Robert Dewar  <dewar@adacore.com>

	* scng.adb: (Check_End_Of_Line): Deal with very long lines

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