Merge pull request #20 from openwebwork/release/2.6

Periodic update from release/2.6 to develop
Added comments to the probability routines.
Added a new routine to generate a list of normally dist. random numbers.
Added routines associated with exponentially distributed random numbers.
Added a routine to calculate the five point summary.
Cleaned up the comments and added info about the optional parameter.
Merge pull request #27 from openwebwork/master

merge release/2.6 as it is merged into master as tag PG-2.7
Added an additional method for calculating the five point summary. The new method includes the median in the calculation of Q1 and Q3 if the median is in the dataset.
Add the initial version of a Sage cell macro.
Added AskSage() subroutine to ask SAGE to do computations during problem authoring.
Merge pull request #30 from aubreyja/ask_sage

Added AskSage() subroutine...
Modification to AskSage() which allows passing  to SAGE's set_random_seed().
Merge pull request #31 from aubreyja/ask_sage

Modification to AskSage() to allows passing $problemSeed to SAGE's set_random_seed()
Fix pgalias bug where files have the same root but different extensions.
Merge pull request #32 from jwj61/develop

Fix pgalias bug where files have the same root but different extensions.
Merge pull request #34 from openwebwork/hotfix1

Stop use of WW1 IO methods. Only use WW2 methods
Merge pull request #29 from drjt/feature/SageMacro

Add the initial version of a Sage cell macro.
Modify debug message
Change tex_cener key to tex_center
Adjust addresses to the .js files to match new organization