Improve error message when opening files

[Federico M Pouzols]

When you try to Load() a file that is not readable you'll get an error like this:

/home/fedemp/test/build-mantid/bin/mantid/simpleapi.pyc in Load(Filename, **kwargs)
     87     algm = _create_algorithm_object('Load')
     88     _set_logging_option(algm, kwargs)
---> 89     algm.setProperty('Filename', filename) # Must be set first
     90     # Remove from keywords so it is not set twice
     91     try:

ValueError: HierarchicalFileDescriptor::isHierarchical - Unable to open file '/home/fedemp/mantid/TrainingCourseData/LOQ48097.raw'

which can be a bit confusing. See how to make it more clear, suggest that you might not have read permission on the file, etc.

[Federico Montesino Pouzols]

Very verbose error msg when unexpected load problem, re #11113

Changeset: 4143b403b1e93b504bdff8cac8882fddf2f12dda

[Federico M Pouzols]

This is being verified as ​pull request #312.

[Federico M Pouzols]

Jenkins, retest this please.

[Federico M Pouzols]

Jenkins, retest this please.

[Dan Nixon]

Merge pull request #312 from mantidproject/11113_improve_error_msg_Load_python

Improve error message when opening files with Load from Python scripts

Full changeset: ​d84d98ca194e1e0968c9c1bf208d3e12c4a877ef

[Stuart Campbell]

This ticket has been transferred to github issue ​11952