For some reason, GCC 4.2.1 ignores casts (for removing constness)
in calls to inline functions.

page_align(), ut_align_down(): Make the parameter const void*, but still
return a non-const pointer.  This is ugly, but these functions cannot be
replaced with a const-preserving macro in a portable way, given that
the pointer argument is not always pointing to bytes.

buf_block_get_page_zip(): Implement as a const-preserving macro.

buf_frame_get_page_zip(), buf_block_align(): Add const qualifiers.

lock_rec_get_prev(): Silence GCC 4.2.1 warnings.

mlog_write_initial_log_record(), mlog_write_initial_log_record_fast(),
mtr_memo_contains(): Add const qualifier to the pointer.

page_header_get_ptr(): Rewrite as page_header_get_offs(), and
implement as a macro that calls this function.