Merge topic branch t/fd into master

A rash of patches which clean up a good part of fd.c. Nothing major
here, mostly simplifications and documentation improvements.

* refs/heads/t/fd:
  fd: Simplify and move for_each_file_in_dir().
  fd.c: Improve error checking of para_mkdir().
  fd: Revamp para_mkdir().
  fd: Improve read_pattern(), rename it to read_and_compare().
  fd: Remove log message from para_munmap().
  fd: Open-code para_chdir().
  fd: Remove file_exists().
  fd: Improve documentation of xwritev().
  fd: Improve documentation of write_all().
  fd: Improve documentation of write_va_buffer().

diff --cc NEWS.md
index a259ef3e140ceeb5649217c903ee6820a973a0f0,598db71fae93734158509fa5f76853ceb09ccb7b..a0484f09d177cb3f7effdd4962650cdce28281ad
--- 1/NEWS.md
--- 2/NEWS.md
+++ b/NEWS.md
@@@ -1,20 -1,6 +1,21 @@@
  NEWS
  ====
  
 +----------------------------------------------
 +0.7.3 (to be announced) "weighted correctness"
 +----------------------------------------------
 +
 +- Old style PEM keys are now deprecated. They still work but their
 +  use results in a run-time warning. The removal of PEM key support is
 +  scheduled for paraslash-0.8.0.
 +- Version 1.0 of the openssl library has been deprecated. A warning
 +  is printed at compile-time on systems which have this outdated version
 +  because it will no longer be supported once paraslash-0.8.0 comes out.
++- A spring cleanup for the senescent code in fd.c.
 +
 +Downloads:
 +[tarball](./releases/paraslash-git.tar.xz)
 +
  -------------------------------------
  0.7.2 (2023-03-08) "optical friction"
  -------------------------------------

diff --cc afs.c
Simple merge

diff --cc client_common.c
Simple merge