Description

If there is an error in the `ns` form, an exception is thrown, which is not caught in `load`. 

For example, with an invalid :only clause;

(ns clj14.myns
(:use
[clojure.core :only seq]))

With the latest Clojure master as of Aug 24 2013, this generates the following exception, with no source file or line number except the one shown in clojure.core:

Exception :only/:refer value must be a sequential collection of symbols clojure.core/refer (core.clj:3854)

You can find a source file in your project if you painstakingly search through the stack trace, but it would be nice if it jumped out at you in the exception itself. 

Patch: clj-939-v4.diff

Approach: The latest patch does not modify the behavior of any other exceptions thrown by the compiler.  The throw-if function is only used in the load-related functions: this patch changes it to throw CompilerException instead of Exception.  As a result, exceptions which occur while loading files will be decorated with file names and line/column numbers.  The line/column numbers are not always accurate (see notes in attachment screen-clj-939.org) but the file names are correct. 

This is an incremental improvement to compile-time error messages, but it does not solve some of the fundamental problems with reporting correct line/column numbers from errors thrown by the compiler. 

Screened by: Stuart Sierra (re-screened by Alex for the specific comments by Rich)