Changes since 2.4.0
1. _pf_set_pf_value: if PF_FORCE_LEARN_MODE ('L') is used, then
   always set this bit for mode values.

Changes since 1.2
1. If a parameter has the value "))cmd", then its value is replaced by 
   the execution of cmd in a shell.
2. pf_get_string modified to take sizeof(buf)

Changes since 1.1
1. Added PF_UINT_TYPE for unsigned ints
2. Updated copyrights, changed few <pfile.h> to "pfile.h"
3. Fixed bug involving access to read-only directories

Changes since 1.0:
1. Symbolic links are traced by file functions.  This is more useful for 
   functions such as pwhich
2. -V flag to pf_open_paramter_file turns on verbose pfile searching.
