Better error msg.
Add comment about tensor.{std,var} method on how we compute it.
Update NEWS.txt with modif since 0.6rc2
Issue #783: python3 compatible - remove relative imports.

This commit starts a series of changes to eliminate relative and redundant imports.

- do not import theano.tests unless theano.test() function is called.
- reuse  TheanoConfigParser instance from configdefaults.
PEP 8 compliance changes.
Merge pull request #1222 from nouiz/fix_gpu_strides_crash

Fix gpu strides crash
Avoid importing theano into itself.
Removed unused imports.
Use absolute imports.
Use absolute imports.
Use absolute imports.
Use absolute imports.
Removed unused imports.
Removed unused imports and converted relative imports to absolute.
Converted relative imports to absolute.
Converted relative imports to absolute.
Converted relative imports to absolute.
Removed unused import.
Removed unused import and converted relative imports to absolute.
Removed unused import and converted relative imports to absolute.