speed improvements

[buzzdee]

The expr command should use { } around its expressions that it evaluates. If I understand the documentation right, since tcl 8.4 this prevents some conversions between strings and numbers.

[buzzdee (sebastia)]

svn revisions 2798-2803 surround expr in whiteboard, xmpp, and jabberlib subdirectories.

[buzzdee (sebastia)]

now, up to svn revision 2808 the remaining expr statements got the {}

I hope I haven't introduced too much subltle errors, therefore testing is needed ;)

I'll mark it as fix committed, if there are problems, please reopen....