build.py -c closure: Show file name and line number of errors and warnings.

[jorix]

When errors or warnings from compilation is more comfortable to see directly where they are produced. Currently must guess the location of the errors using OpenLayers.js obtained by build.py -c none.

To obtain this feature is necessary pass to the compiler a list of filenames instead of the merged file.

The implementation proposes to use  jscompiler.py used in the Closure Library. Changes are proposed in mergejs.py so can return a merged file or a list of files, but has remained the same code for the selection and determine order of source files. There are also changes in build.py

[jorix]

Please review this pull request:

 https://github.com/openlayers/openlayers/pull/49

Tested on: Windows XP+python2.4, Vista+python2.7 and Ubuntu10+python2.6

[jorix]

Please review:

 https://github.com/openlayers/openlayers/pull/91

This pull request replaces the  #49 that had many commits.

[jorix]

 https://github.com/openlayers/openlayers/commit/08d951c02f10d8415a365765716708e1e45836d4