#111 distinguish tcllib man pages from other packages

[Larry W. Virden]

When a Tcl extension installs, care needs to be taken
that the manual pages do not overwrite pages from some
other package.

To do this, perhaps it is necessary to install man
pages to match
the namespace of the module:

struct::tree.n

for instance - or, if the :: are a problem , then perhaps
struct_tree.n

[Andreas Kupries]

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I found out through a second bug report that tree was not just
used here out of thin air, but is in conflict with a BLT
manpage. Fixed that.

The topic in general is something we have to hash out among
all of us, on tcllib-devel. This should be kept on radar for after
the 1.4 release.

For the 1.4 release I prefer specific bug reports about clashes
we can fix immediately.