Previously test allocator only guaranteed alignment enough for a pointer.

On some platforms (e.g. SPARC) double has to be aligned to 8 bytes but pointers
can have a size of 4 bytes. This commit increases allocation header to fix that.

In practical terms the allocation header is now always 8 bytes.

This fixes tests in PUGIXML_NO_XPATH mode on SPARC64 (#48).

SPARC does not allow unaligned accesses - e.g. you can't read an unaligned int.
Normally pugixml does not perform unaligned integer/pointer accesses, but page
heap can allocate blocks that are not aligned so that we can detect a single-
byte read/write overrun.

Additionally, the hardcoded page size we're currently using is really system
specific - on SPARC the page size can be 8 Kb instead of 4 Kb so mprotect can
fail.

Address sanitizer can detect underflows so we don't really need the custom
allocator.

Additionally, custom allocator can return memory that is not pointer-aligned;
this causes undefined behavior sanitizer to complain.

Switch to malloc and manually aligning the pointer to the page boundary.

mmap is much slower than malloc; this change makes tests ~4x faster.

Rename PAGE_SIZE to page_size to avoid define conflict with Android SDK.
Minor fixes in several tests.

Align allocations to right end of page boundary to catch buffer overruns,
instead of unmapping on deallocations mark the page as no-access to guarantee
a page fault on use-after-free.

This should never happen but can improve debugging experience for
work-in-progress changes since that avoids memcpy() into negative memory
space (debugger can't backtrace from failed memcpy since it does not set
up the stack frame).

git-svn-id: https://pugixml.googlecode.com/svn/trunk@1070 99668b35-9821-0410-8761-19e4c4f06640

git-svn-id: https://pugixml.googlecode.com/svn/trunk@1030 99668b35-9821-0410-8761-19e4c4f06640

git-svn-id: http://pugixml.googlecode.com/svn/trunk@834 99668b35-9821-0410-8761-19e4c4f06640

Enabled many additional GCC warnings (most notably -Wshadow and -Wold-style-cast), fixed the code accordingly

git-svn-id: http://pugixml.googlecode.com/svn/trunk@800 99668b35-9821-0410-8761-19e4c4f06640

git-svn-id: http://pugixml.googlecode.com/svn/trunk@711 99668b35-9821-0410-8761-19e4c4f06640

git-svn-id: http://pugixml.googlecode.com/svn/trunk@623 99668b35-9821-0410-8761-19e4c4f06640

git-svn-id: http://pugixml.googlecode.com/svn/trunk@607 99668b35-9821-0410-8761-19e4c4f06640

git-svn-id: http://pugixml.googlecode.com/svn/trunk@602 99668b35-9821-0410-8761-19e4c4f06640

git-svn-id: http://pugixml.googlecode.com/svn/trunk@383 99668b35-9821-0410-8761-19e4c4f06640