The old code was breaking strict aliasing rules.

Signed-off-by: Piotr Sikora <piotr@aviatrix.com>

When graceful shutdown was requested, and then nginx was forced to
do fast shutdown, it used to (incorrectly) complain about open sockets
left in connections which weren't yet closed when fast shutdown
was requested.

Fix is to avoid complaining about open sockets when fast shutdown was
requested after graceful one.  Abnormal termination, if requested with
the WINCH signal, can still happen though.

rand() is used on win32. RAND_MAX is implementation defined. win32's is
0x7fff.

Existing uses of ngx_random() rely upon 0x7fffffff range provided by
POSIX implementations of random().

MTU selection starts by doubling the initial MTU until the first failure.
Then binary search is used to find the path MTU.

This fixes potentially incorrect cache size calculations and non-working
"min_free" when using cache in directories with non-ASCII names.

Just a drive letter might not correctly represent file system being used,
notably when using symlinks (as created by "mklink /d").  As such, instead
of trying to call GetDiskFreeSpace() with just a drive letter, we now always
use GetDiskFreeSpace() with full path.

Further, it looks like the code to use just a drive letter never worked,
since it tried to test name[2] instead of name[1] to be ':'.

This makes it possible to use temporary directories with non-ASCII characters,
either explicitly or via a prefix with non-ASCII characters in it.

This makes it possible to upload files with non-ASCII characters
when using the dav module (ticket #1433).

This makes it possible to delete files with non-ASCII characters
when using the dav module (ticket #1433).