Changes to multicolvar/rt-histogram because original version
considered first frame when calculating histogram.  This version
ignores first frame in trajectory.  I checked against a modified
version of the old version in which the first frame is ignored and
the two codes give the same results

[makedoc]

I changed the scripts to build the manual (and the vim script stuff) so that
they always use the locally compiled plumed. I think this is more consistent,
especially when one has already installed plumed and is installing it
again to a new location.

useful for macports

[makedoc]

I implemented a shell-only tool "plumed config"

This tool can be used to probe the src/config/config.txt
configuration file.

So far it can be used e.g. as
plumed config has mpi
to enquire for an enabled feature.

It has some advantage wrt the --has-xxx options:

1. It is based on file src/config/config.txt,
which parses configure.ac and header files to find possible -D
and Makefile.conf to find activated -D.
This means that it is not necessary to manually
edit the src/config/Config.h and src/core/CLToolsMain.cpp
file to add new defines

2. it is shell only, thus works in cross compiled environment

This is a textual file that contains all the configuration info.

It should be easier to parse from scripts.

[makedoc]

Now works also when plumed has been installed with a different name

[makedoc]

- METAD: exit with error if used
- PBMETAD: gives a warning and deactivate the interval for the specific variable
close #181

Added an option in OFile to enforce backup of files even if restarting