Patch from Nils Goroll

Patch by Nils Goroll

Patch from Nils

we hit the null terminator for a string in a STRING_LIST

Patch by Nils

special case where the encoding and decoding are the same

Patch by Nils Goroll <nils.goroll@uplex.de>

This removes some switch/case clutter at a slight potential cost for
the additional indirection.

This partly reverts my previous commit 78ac8836,
which was wrong:

Varnish is massively multithreaded, so all vmods must be thread-safe.

While it is possible to write thread-safe vmods without pthreads support,
some systems (like those of the Solaris-heritage) need additional compiler
flags for MT support (-D_REENTRANT -pthreads). To avoid weird potential
issues, we should, by default, include full MT support.

Also, libpthreads is available for vmods because varnishd itself links
against it, but, again, making this dependency explicit should be the right way.

/usr/bin/env python in vmodtool.py does not work for cases where it's called
python$VERSION, e.g. python2.7 - as is the case on SmartOS with pkgin