* arts-2-1-550

* src/absorption.cc, src/continua.cc, src/m_abs.cc,
src/m_abs_lookup.cc, src/m_atmosphere.cc, src/m_batch.cc, src/m_rte.cc:

Revise all OpenMP loops. Make sure loops have enough iterations before
parallelizing them. Otherwise it can really hurt performance.
Basically now all loops require the number of iterations to be greater
or equal to the maximum number of threads (some exceptions such as
ybatchCalc). Here are some benchmarks:

make check (TEST_JOBS=4)

ubuntu5 before: 29 sec
ubuntu5 after : 18 sec

ubuntu1 before: DNF (stuck in fast.doit)
ubuntu1 after:  13 sec

ctest -j4 -R xmldata -E isoratios

ubuntu5 before: 43 sec
ubuntu5 after:  17 sec

ubuntu1 before: 22 sec
ubuntu1 after:  15 sec

ubuntu5 uses gcc 4.4.4, ubuntu1 gcc 4.6.3

* src/m_abs.cc (abs_xsec_per_speciesAddLines,
abs_xsec_per_speciesAddLines), src/m_cia.cc
(abs_xsec_per_speciesAddCIA): Only output to out3/2 if visible.

git-svn-id: https://www.sat.ltu.se/svn/rt/arts/trunk@8295 aaf1aab0-4228-0410-ad68-8dceda47f409