Revised/clarified some comments w.r.t mRGBE encoding, wavelet xform.

Disabled bin reallocation in getPreCompContribByMod() when loading contrib
pmap with rcontrib if the bins don't match, as this caused corrupted output
streams, and there's no easy way to reassign these if the binning changes.
Consequently, rcontrib now just bails out in this case, indicating the -bn
option the user has to supply by hand. UGLY and stupid, but it'll have to do
for now.

Added support for biorthogonal 3.1 wavelet via WAVELET_BIOR compile option
for testing and comparison against Daubechies 2, as it is near-symmetrical,
but otherwise not really better.

Added output stream parameter to dumpCoeffs2() to optionally dump wavelet
coeffs to a file during unit testing.

Added WAVELET_TEST_LOG compile option to test log encoding independently of
pmapcontrib.h in wavelet unit test.

Added option 6x6 approx wavelet coeffs at coarsest level, instead of 3x3
(see WAVELET_PADD2_MINLEN) after noticing pywavelets omits the last xform
step. The test results are inconclusive however (no clear adavantage) and
they require significantly more storage since never thresholded.

Realised WAVELET_EXTEND_GRAD1 is a dumb idea with log encoded data, since
it assumes linear input. Added warning in comment.

Added WAVELET_TEST_INIT option 7 in wavelet unit test to load reference
rcontrib data from a text file.