Rename dec/inc_weak_task_count to inc/dec_live_count and remove register_task/unregister_task. Closes #4768
Add debug info tests
fix typos in sample code, add enum to json encoder, add test case
json bugfixes
tidy
json bugfix
json add enum encoder test case
re-special-case Option in JSON encoding
json tidy
added issue for reference in FIXME
mk: Typo
mk: Run debuginfo tests by default, but only if gdb is available
libcore: LinearMap doesn't need to pass around the bucket vec
core: rename hashmap test functions
core: add LinearMap::find_or_insert{,_with}

This allows for inserting a new value into the map only if it doesn't
already exist in the map.
Add NumCast trait for generic numeric type casts
core: Fix dec/inc_kernel_live_count mixup
core: Rewrite last_os_error in Rust for unix and provide access to errno (unix) and GetLastError (windows).
core: Rewrite last_os_error in Rust for windows as well.
rt: remove last_os_error and adjust tests.