ERR_set_mark, ERR_pop_to_mark - set marks and pop errors until mark
ERR_set_mark() sets a mark on the current topmost error record
if there is one.
ERR_pop_to_mark() will pop the top of the error stack until a
mark is found. The mark is then removed. If there is no mark, the whole
stack is removed.
ERR_set_mark() returns 0 if the error stack is empty,
ERR_pop_to_mark() returns 0 if there was no mark in the error
stack, which implies that the stack became empty, otherwise 1.
ERR_pop_to_mark() were added
in OpenSSL 0.9.8.