Closes #21665: Don't use OPTS=noxp or -DWINVER=0x0500 when compiling Tcl/Tk
on the buildbots.

2.7 does still support Win2k, but using those options makes default ttk ugly
while not using them doesn't seem to break Win2k.
Fix minor typo in round docs.  Reported by Scott Hinton on docs@.