Sort the names of plugins.

Sort the names of plugins in the documentation. Upon visual inspection, also fix a number of formulas and text issues found in the manual's description of the various plugins.
Make sure the postprocessor can also work in case we use a direct solver, where pressure and velocity dofs reside in the same block.
escape angle brackets in parameters.tex

Note that we can not replace all occurences of < by $<$ because this
will break if we are already inside a math formula.
Use a lower degree quadrature and explain why.
Merge pull request #92 from bangerth/fix-pressure-postprocessor

Fix pressure postprocessor
Merge pull request #101 from tjhei/escape_angle_brackets

escape angle brackets in parameters.tex
add .prm.out files to make eclipse happy

Even though the .out files get generated by the Makefile in doc/ when
you build manual.pdf, it turns out eclipse is complaining when the .out
files are not present.
Also remove the .out from .gitignore again and do not generate a .out
for doc/manual/empty.prm because it is not used.
Add remove 'all' as a possibility for model names and other plugins.
Merge pull request #102 from bangerth/fix-defaults

Add remove 'all' as a possibility for model names and other plugins.
multiplex output

All output is now also put into output/log.txt in addition to the
screen.

Some error messages are now only printed on processor 0 instead of on
every processor.

The header should be printed in case of early failure (for example no
prm given), but also piped into the output file. For that reason it now
lives in global.h. Update the version script to find the version info.
update changes.h
Merge pull request #103 from tjhei/multiplex_output

multiplex output
Do not create output from processes != 0 if there is an error in the input file.
Write a changelog entry.