merge: trivial tidying

 * clang-format
 * rename variables: descrip -> desc
 * rename variables: buffer -> buf
 * rename variables: command -> cmd
 * rename variables: progressbar -> progress
 * rename variables: thepid -> pid
 * rename variables: synch -> sync
 * name macro variables
 * lowercase local variables
 * expand meaningless R_BOTH macros
 * tidy mutt_edit_content_type()
 * tidy generate_body()
 * tidy mutt_alias_create()
 * small code tidying
 * boolify variables/params
 * reduce variable scope