Faster debug version

[seanshpark]

As new eval has landed, one small problem is that debug version execution has became very slow.
Can there be some level of checking so that it might be somewhat faster for debugging?

[ILyoan]

It seems like rcs_chunked_list_t::get_prev() and rcs_chunked_list_t::get_next() are called too many times in debug mode. The prominent caller of them are assert_node_is_correct() and assert_list_is_correct().

[ruben-ayrapetyan]

/CC @sand1k

[sand1k]

Surrouned code of assert_list_is_correct(), assert_node_is_correct() and rcs_recordset_t::assert_state_is_correct() with #ifdef JERRY_HEAVY_DEBUG ... #endif, so that this checks run only for unit tests.
Pull request #193 performs the update.

[seanshpark]

Nice!