Guard against extracting a gcd for symbolic powers.

Fixes issue 4032: trigsimp() TypeError: symbolic boolean expression has no truth value
http://code.google.com/p/sympy/issues/detail?id=4032
Add test from issue 4032.
fixed documentation bug as per issue #4029
Add test for issue 3400
Add test for issue 2826
Add _eval_nseries method for expint()
Some tests for expint series
Merge pull request #2495 from perseus0807/4029_iterables

fixed documentation bug as per issue #4029
Add Vinit Ravishankar to AUTHORS/aboutus. Welcome to SymPy!
Merge pull request #2511 from smichr/auth

Add Vinit Ravishankar to AUTHORS/aboutus. Welcome to SymPy!
Merge pull request #2505 from skirpichev/2958-series-for-error_functions.py

Implement missing series methods for exponential integrals (first part of the issue 2958)
Doc changes
Rectified errors in docs
Merge pull request #2501 from skirpichev/3400-test

Add test for issue 3400
Merge pull request #2509 from srjoglekar246/motionparamdocs

Doc changes to functions.py
Merge pull request #2503 from skirpichev/2826-test

Add test for issue 2826
Merge pull request #2489 from jrioux/relational

Guard against extracting a gcd for symbolic powers.

Fixes issue 4032: trigsimp() TypeError: symbolic boolean expression has no truth value
http://code.google.com/p/sympy/issues/detail?id=4032
Add numeric computation doc page

Discusses lambdify, ufuncify, and Theano options for numeric evaluation
add link to numeric computation in modules index
replace x.length with n