ENH: handle odd c-shell sourcing patterns

- the result of lsof, which is used in the etc/cshrc to locate the
  installation, may contain trailing information about host and mount
  point.

  There is also a moderate concern with people sourcing the
  file indirectly with their own version in the same directory.
  For example, a 'etc/cshrc-site' that actually sources 'etc/cshrc'.
  This leads to multiple matches in the lsof output, so we only take
  the first one, stop there and hope they didn't do something even
  trickier.