Rename dec/inc_weak_task_count to inc/dec_live_count and remove register_task/unregister_task. Closes #4768
Add debug info tests
core: Remove GenericChan/Port from prelude. Closes #4762
make Option's iter method use a lifetime
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 files that needed GenericChan/Port from prelude
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.
Long lines.
rt: remove last_os_error from rustrt.def.in
Revert "librustc: Make monomorphic newtype structs work cross-crate"

This reverts commit a8f039a085c7d7622899b7a4d1bebfe2d7621165.
auto merge of #4867 : z0w0/rust/pruneprelude, r=catamorphism
auto merge of #4874 : thestinger/rust/option, r=catamorphism