Bad error message for missing module in --make

GHC --make uses getImports to find the imports of a 
module.  It has two bad flaws

a) it's a total hack, parsing the file character by 
character, which is really slow.   We though it stopped 
after the import statements but it doesn't; it chunters 
through the entire file

b) It does not record line numbers, so if the imported 
module does not exist, there is no decent error message

We have a plan; this bug report makes sure we don't 
forget.

Trac metadata

Trac field	Value
Version	6.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	ResolvedFixed
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 3

added Tbug Trac import labels

Attached file Boo.2.hs ($24).

changed title from ghc --make import searching broken to Bad error message for missing module in --make

Logged In: YES 
user_id=48280

Partially fixed, (b) still to do.

closed

Logged In: YES 
user_id=48280

Fixed.  We still don't report the line number, but it's good
enough.

mentioned in commit fc4c9683

added Plow label