Add trellis for DC

Add option to apply trellis quantization to the DC coefficients ( see
#57 ). May need further refinement to make sure block order during
trellis optimization matches order during coding.
Add option to split DC scans

Command line option -split-dc-scan is added to code DC scans
independently (instead of interleaved). It should be determined whether
this option introduces any decoder compatibility issues ( see #83 )
Option -multidcscan is renamed to -opt-dc-scan
Fix issue with DC trellis
yuvjpeg: fix trivial leak

Cherry-picked from daala 91c1dfd8ec30fda886c31f00678eaf074e3e4a6c
Merge pull request #92 from tmatth/fix_yuvjpeg_leak

yuvjpeg: fix trivial leak
Add error checks for malloc calls that don't already have them. Issue #87.
Get rid of unnecessary and obsolete platform configuration instructions.
Fix issue with scan printout

Incorrect values of scan parameter Al were printed out in verbose mode
Implement DQT merging

See #30.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Merge pull request #88 from dwbuiten/dqtmerge

Implement DQT merging
Merge branch 'dctrellis'
Update cjpeg usage text