Added Stout `path::normalize` function for POSIX paths.
Added Stout `path::normalize` function for POSIX paths.

Added `path::normalize` to normalize a given pathname and remove
redundant separators and up-level references.

This function follows the rules described in `path_resolution(7)`
for Linux. However, it only performs pure lexical processing without
touching the actual filesystem.

Review: https://reviews.apache.org/r/65811/

Gilbert88/mesos,abudnik/mesos,dforsyth/mesos,chhsia0/mesos,abudnik/mesos,reneploetz/mesos,chhsia0/mesos,jpeach/mesos,jpeach/mesos,gsantovena/mesos,gsantovena/mesos,chhsia0/mesos,Gilbert88/mesos,reneploetz/mesos,jpeach/mesos,Gilbert88/mesos,reneploetz/mesos,kaysoky/mesos,gsantovena/mesos,dforsyth/mesos,Gilbert88/mesos,kaysoky/mesos,abudnik/mesos,gsantovena/mesos,reneploetz/mesos,jpeach/mesos,Gilbert88/mesos,kaysoky/mesos,abudnik/mesos,dforsyth/mesos,kaysoky/mesos,jpeach/mesos,chhsia0/mesos,abudnik/mesos,kaysoky/mesos,jpeach/mesos,gsantovena/mesos,dforsyth/mesos,Gilbert88/mesos,kaysoky/mesos,dforsyth/mesos,dforsyth/mesos,abudnik/mesos,kaysoky/mesos,reneploetz/mesos,Gilbert88/mesos,reneploetz/mesos,abudnik/mesos,chhsia0/mesos,jpeach/mesos,gsantovena/mesos,chhsia0/mesos,dforsyth/mesos,reneploetz/mesos,chhsia0/mesos,gsantovena/mesos