... as well as some cleanup (some commented-out code is left to
support UxTradMsg again is someone really complains ;)).

- saved gettimeofday() calls in imtcp (and increased reception buffer)
- somewhat optimized stringbuf.c
- some other optimizations

Well, actually this and a lot of related things. I improved the
testbench so that the new capabilities are automatically tested and
also did some general cleanup. The current multiple tcp listener
solution will probably receive some further cleanup, too, but looks
quite OK so far. I also reviewed the way tcpsrv et all work, in
preparation of using this code for imdiag. I need to document the
findings, especially as the code is rather complicated "thanks" to
the combination of plain tcp and gssapi transport modes.

removed some warning in imklog compilation, but may not have
solved a lurking issue (but placed comment so that we know if
something surfaces)

to make sure only the minimum number of file handles is left open
during a exec call. This is not a 100% solution, as there are also
some fopen() calls and, more importantly, file descriptors opened
by libraries. But it is better than nothing (and it was quick, at
least until we run into platform hell, what we will for sure ;)).

pkg-config uses uppercase for its _CFLAGS and _LIBS variable names.
So we follow suit and convert all _cflags and _libs variables to
uppercase for more consistency.

...this improves performance and consistency and also fixes
a bug where subsecond time properties generated by imfile, imklog and
internal messages could be slightly inconsistent.

- added message property "inputname", which contains the name of the
  input (module) that generated it. Presence is depending on suport in
  each input module (else it is blank).
- added system property "$myhostname", which contains the name of the
  local host as it knows itself.

The limit can now be set via $MaxMessageSize global config
directive (finally gotten rid of MAXLINE ;))