fil2h5, h52fil, dice, and bl_scrunch can mangle the output file name

[texadactyl]

In fil2h5, it is possible to mangle the output file name if the input file path has an embedded "fil". In essence, the embedded "fil" will be inadvertently changed to "h5". E.g. "abc.filter.def.fil" --> "abc.h5ter.def.h5" (should be "abc.filter.def.h5"). This was caused by misuse of the string replace function.

Solution:

• utils.change_the_ext(path, old_ext, new_ext) will change only the final old_ext in the path or append the new_path if there is no old_ext present.
• fil2h5, h52fil, dice, and bl_scrunch call the new function.
• Since the function is generic, it can also be leveraged by other projects such as turbo_seti (probably needed!).