Rename bunch of source files to more consistently use dashes
instead of underscores to connect words.
* sb/filenames-with-dashes:
replace_object.c: rename to use dash in file name
sha1_file.c: rename to use dash in file name
sha1_name.c: rename to use dash in file name
exec_cmd: rename to use dash in file name
unicode_width.h: rename to use dash in file name
write_or_die.c: rename to use dashes in file name
