bootchart: various superficial cleanups

Let's update bootchar to share the coding style a bit more with the rest
of the package.

- Some tabs/spaces fixes

- add #pragma to header

- split up header so that we have a 1:1 relation between .c and .h files
  like everywhere else

- Prefix user command line arguments/configuration settings with "arg_".

- other coding style fixes
bootchart: bump RLIMIT_NOFILE only after we forked us off, so that the init system inherits the kernel default