SFM: use old avec implementation in PBA

to avoid copying in avec::set
Merge pull request #117 from Waldteufel/sfm-old-avec

SFM: use old avec implementation in PBA
MATH: Matrix SVD and QR implementation and test cases
MATH: Matrix SVD sorting of eigenvalues, more test cases
[draft] throw out lots of code
[disable omp in pba]
[draft] allow more loops to be parallelized
[draft] annotate auto-vectorization
[scratch] attribute optimization
[scratch] more openmp
[draft] more openmp
[scratch] more timing information
[scratch]
[scratch] remove some unreachable code
added video initial pair search
added SIFT write function
further adjustments for sift files