libcap: Update to 2.50

libcap: Update to 2.50

- Update from 2.49 to 2.50
- Update rootfile
- Version 2.50 failed to install capsh - bug raised for this
   https://bugzilla.kernel.org/show_bug.cgi?id=213261
   patch to fix this bug created and used in this build
- Changelog
   Release notes for 2.50
    2021-05-24 12:05:16 -0700
      Some new capsh features:
          --explain=cap_foo: describe what cap_foo does (Bug 212451)
          --suggest=phrase: search all the cap descriptions and describe those that match the phrase
      Add "keepcaps" module argument support to pam_cap.so (reported by Zoltan Fridrich. Bug 212945)
          extend libcap to include cap_prctl() and cap_prctlw() functions to regain feature parity with Go "cap" package. These are only needed when linking against -lpsx for keepcaps POSIX semantics.
          this likely requires substantial application changes to make Ambient capability support usable in general, but doing our part for the admin.
      Add a test case for recent kernel fix (Bug 212737)
      Go pragma fix for convenience functions in "cap" module (reported by Lorenz Bauer. Bug 212321)
      Minor man documentation updates
      Minor build tree improvements (mostly for maintainer)

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>