Added MX(int,int) and MX::isNullE() for non-disruptive implementation of #380
Added MX::addToSum convencence function, #380
Made reverse mode derivative propagation use addToSum instead of +=, #380
Made reverse mode derivative propagation use addToSum instead of += (2), #380
Made reverse mode derivative propagation use addToSum instead of += (3), #380
Disallowed MX() += A, MX() -= A, #380
Concerning #1004: first pass of SWIG cleanup.
Removed all specializations of meta::couldbe.
Making vector in Python a feature minimal type,
instances of vector are now all converted to lists,
const refs or refs of vectors are now copies in python.
Update nlp.py
Repair haskell interface generation
MX::isNull --> MX::isNullE in MXFunctionInternal, #380
MX::isNull --> MX::isNullE in CallFX, #380
MX::isNull --> MX::isNullE in mx_tools, #380
MX::isNull --> MX::isNullE in FXInternal, #380
MX::isNull --> MX::isNullE in XFunctionInternal, #380
Changed default constructor of MX to return a 0-by-0 matrix instead of a null pointer, #380
Removed helper functions for #380
Removed Matrix::isNull, fixed broken unit tests, #380
Simplifications in MXFunctionInternal, post #380
Simplifications in MX, post #380
Simplifications in MXNode, post #380, refactored MXNode destructor