Log Message:
mpfr: update to 4.0.2.

Changes from version 4.0.1 to version 4.0.2:
- Corrected minimal GMP version in the INSTALL file and the MPFR manual.
- Option -pedantic is now always removed from __GMP_CFLAGS (see INSTALL).
- Shared caches: cleanup; really detect lock failures (abort in this case).
- Improved MPFR manual. In particular, corrected/completed the
  mpfr_get_str description in order to follow the historical behavior
  and GMP's mpf_get_str function.
- Bug fixes (see ChangeLog file).