Extract unknown meta-data variables

For Alceste files, we need to import variables whose names
are not known in advance. This can also be theoretically
useful for other sources. Also do not import DateTimeStamp for
Alceste files as it corresponds to the import time, and
select all variables by default.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/r-temis@522 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Require tm >= 0.5-10

Not strictly needed, but import plug-ins need it,
and automatic installation will fail when trying to
load the new tm while the old one is already loaded.
Better make R install the new one when installing
RcmdrPlugin.temis.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/r-temis@523 edb9625f-4e0d-4859-8d74-9fd3b1da38cb