Bug in Makefile.in

This line
```
install_sh_DATA = $(install_sh) -c -m 644
```

uses the flag `-c`, however, according to `man install` the flag doesn't do anything.  Should this be `-C` instead?
```
       -c     (ignored)

       -C, --compare
              compare each pair of source and destination files, and in some cases, do not modify the destination at all
```