print page dump

buf_page_print(): Remove the ut_ad(0) from the beginning. Add two flags
(enum buf_page_print_flags) that can be bitwise-ORed together:

BUF_PAGE_PRINT_NO_CRASH:
  Do not crash debug builds at the end of buf_page_print().
BUF_PAGE_PRINT_NO_FULL:
  Do not print the full page dump. This can be useful when adding
  diagnostic printout to flushing or to the doublewrite buffer.

trx_sys_doublewrite_init_or_restore_page(): Replace exit(1) with ut_error,
so that we can get a core dump if this extraordinary condition happens.

rb:924 approved by Sunny Bains