Remove our realpath implementation from pextlib

[ryandesign (Ryan Carsten Schmidt)]

pextlib1.0 contains an implementation of realpath, to work around a bug in the versions of Tcl (8.4.7) shipped in Mac OS X Leopard and earlier:

• macports-base/src/pextlib1.0/realpath.c​
• macports-base/src/pextlib1.0/realpath.h​

MacPorts bundles a copy of Tcl 8.5 now, and the bug was fixed in Tcl 8.4.10 according to comment:ticket:21082:15, so that reason should no longer apply and perhaps this code could be removed. We should verify that the problem that it fixed on Leopard and earlier (#21082) remains fixed if the code is removed. (Is there a test for it?)

[jmroot (Joshua Root)]

It still has its uses.

% file normalize /opt/local/include/SQLite3.h
/opt/local/include/SQLite3.h
% realpath /opt/local/include/SQLite3.h
/opt/local/include/sqlite3.h