The matrix g  can have CV_32F or CV_64F type,  but g.at uses only float template.
This fix adds specialization for double type.

Overloaded PCA constructor and ( ) operator to implement Feature#2287 - PCA that retains a specified amount of variance from the data. A sample was added to samples/cpp to demonstrate the new functionality. Docs and Tests were also updated

added COVAR_ and SORT_ enums to core.hpp; fixed many, many VS2005, VS2010 and MinGW (GCC 4.5.2) warnings

replaced "const InputArray&" => "InputArray"; made InputArray and OutputArray references. added "None()" constant (no array()).

a big patch; use special proxy types (Input/OutputArray, Input/OutputArrayOfArrays) for passing in vectors, matrices etc.

added IPP dot product functions. Only 32f data type supported for now (there are accuracy issues in 8u/16s/16u/32s functions which will be fixed in IPP 7.0.3)

replaced alloca() (a.k.a. cvStackAlloc) with AutoBuffer or vector() everywhere. cvStackAlloc() is still defined, but we do not need alloca() anymore to compile and run OpenCV (fixes #889 and may be some others)

added hconcat & vconcat functions for joining matrices; moved some inline functions out of the headers; fixed several bugs in documentation; removed MatND from docs