Expand globs to zero arguments (nullglob) only for set, for and count.
The warning about failing globs, and setting the accompanying $status,
now happens regardless of mode, interactive or not.
It is assumed that the above commands are the common cases where
nullglob behaviour is desirable.
More importantly, doing this with `set` is a real feature enabler,
since the resulting empty array can be passed on to any command.
The previous behaviour was actually all nullglob (since commit
cab115c8b9), but this was undocumented;
the failglob warning was still printed in interactive mode,
and the documentation was bragging about failglob behaviour.
Rather than returning a list of productions and an index,
return the relevant production directly from the rule function.
Also introduce a tag value (replacing production_idx) which tracks
information like command decorations, etc. with more clarity.
This change eliminates global variables like stdout_buffer. Instead we wrap up
the IO information into a new struct io_streams_t, and thread that through
every builtin. This makes the intent clearer, gives us a place to hang new IO
data, and eliminates the ugly global state management like builtin_push_io.
This change moves source files into a src/ directory,
and puts object files into an obj/ directory. The Makefile
and xcode project are updated accordingly.
Fixes#1866