add hough_circle() to vipsCC and python

now exposed to Python and C++
oops in vips_scale()
definition oops
small oopes

thank you clang
add Travis CI config

thanks Lovell
start fixing up the auto-decode stuff
auto-decode to lab, not labs

helps in many places
complex lut was broken
longer stall time for ahead-threads

we must stall for AGES occasionally, really the stall time is about
enforcing a certain thread ordering
wrap im_*merge() as a class
im_*merge() class wrapper works
wrap im_*mosaic() as classes
vips_mosaic() outputs mosaic params
wrap im_match*() as a class
more hackery
match works
wrap im_global_balance*() as a class
wrap im_remosaic() as a class
redo im_*mosaic1() as classes
redo im_*merge1() as classes