This is one of those stupid Tcl mistakes that an experienced Tcl
programmer just wouldn't make. We should always use eq and ne to
compare string values (and never == or !=) as when we use ==/!=
Tcl will attempt to convert either side to numeric if one of the
two sides looks like a numeric. This could cause some trouble if
a file named "1" exists and a different file named "1.0" also exists;
their paths are equal according to == but not according to eq.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>