275 prerelease

Hi all,

Commit 751728562ff124ede3386c26925fa06edc8862fd is available for testing, with a view toward releasing 275.

Draft release notes:

                                    TXR 275
                                   2022-04-??

  Features

  - Hashing: new group-map function: group-reduce with
    built-in map pass.

  - Lib: new isecp function: test whether two sequences
    intersect without calculating intersection.

  - FFI:
    - intmax-t and uintmax-t types.
    - new str-s, bstr-s and wstr-s types for receiving foreign
      string without freeing its memory.
    - after a FFI call, the arguments are processed for 
      reverse data flows and memory clean-up in reverse order.
    - with above two features, strtol can be wrapped in FFI,
      including the error-reporting char **end pointer.
  
  - Loading: new *load-search-dirs* variable.
    - default search directory list includes sysrooted lib dir

  Bugs
  
  - configure: minor escaping corner cases in in production of
    ./reconfigure script.
  - compiler: package-related bug in file-compilation, reported
    by Paul A. Patience. 
  - load: regression: do not try adding suffixes to a path
    which exists; try the given path before anything else
    - Reported by Paul A. Patience.
  - sh, run, open-command and open-process now flush *stdout*
    in situations when it makes sense, standard output is
    ordered between the subprocesses and the parent.