This change sets ParserMode=AllErrors so that the parser is never
allowed to discard the AST and use a dummy one just because it saw too
many errors.
Also, change (*loader.Program).PathEnclosingInterval so that other
clients that forget to set this flag don't panic while calling
fset.File(f.Pos()).Base() on an ast.File f with no position info.
Change-Id: Ie544f169d367d2aa85426212b27063dc72e36fb1
Reviewed-on: https://go-review.googlesource.com/10290
Reviewed-by: Robert Griesemer <gri@golang.org>
3d1847243e