Added missing comma from fuser(1)

Actuallly it was a missing R because \f, shows nothing but \fR, shows a
comma.
Bug-Debian: http://bugs.debian.org/702391
pstree uses COLUMNS environement variable

pstree previously only used the window size for determining number of
columns, then a default of 132. With this change, pstree now checks
the COLUMNS environment variable first and uses that if valid.

env checking code nicked from top.c, by Jim Warner.

Bug-Debian: http://bugs.debian.org/717017