Previously, using m_option_type_alias required that the alias have the
full name of the option value. This is limited if you are reusing the
same opts struct in different sub options. Fix this by add an additional
field to m_option to signal whether or not prefixes should be taken into
account for the alias option. Instead of blindly using whatever is
stored in opt->priv as the name, we can construct the desired option
name for either case (using the prefix or not).
Try to remove m_config implementation details from m_config_frontend.
Not sure if I like it. Seems to be ~100 lines of awkward code more, and
not much is gained from it. Also it took way too long to do it, and
there might be bugs.
Move the "old" mostly command line parsing and option management related
code to m_config_frontend.c/h. Move the the code that enables other part
of the player to access options to m_config_core.c/h. "frontend" is out
of lack of creativity for a better name.
Unfortunately, the separation isn't quite clean yet. m_config_frontend.c
still references some m_config_core.c implementation details, and
m_config_new() is even left in m_config_core.c for now. There some odd
functions that should be removed as well (marked as "Bad functions").
Fixing these things requires more changes and will be done separately.
struct m_config is left with the current name to reduce diff noise.
Also, since there are a _lot_ source files that include m_config.h, add
a replacement m_config.h that "redirects" to m_config_core.h.
