Change the default remove/rename calls to flush the enclosing directory.

Simplify the pluggable file system API by replacing the directory-sync method
with "durable" boolean argument to the remove, rename and open-file methods.

* Add "durable" arguments to relevant functions so that each remove or rename
call specifies its durability requirements.

* Switch the  WT_FILE_SYSTEM::fs_open_file type enum from WT_OPEN_FILE_TYPE,
with WT_OPEN_XXX names, to the WT_FS_OPEN_FILE_TYPE, with WT_FS_OPEN_XXX
names.

Switch the  WT_FILE_SYSTEM::fs_open_file flags from WT_OPEN_XXX names to
WT_FS_OPEN_XXX names.

* Replace the "bool durable" argument to WT_FILE_SYSTEM.fs_remove and
WT_FILE_SYSTEM.fs_rename with a "uint32_t flags" argument, and the
WT_FS_DURABLE flag.

* Remove a stray bracket.

(cherry picked from commit 11f018322c3f84552f2b1fe79f2ca9d6585577fb)

No longer support setting the statistics_log path in WT_CONNECTION::reconfigure.
No longer support setting a custom name for statistics files, only allow a destination directory.
Be more explicit about which logging configuration options are allowed in WT_CONNECTION::reconfigure.

The aim of these changes is to avoid situations where applications that embed WiredTiger allow their users to overwrite unexpected files on a file system.

This potentially requires an upgrade step for applications that were specifying a non-standard file name component for statistics log file names, it's not backward compatible.
(cherry picked from commit 9cc5d0f4b18753c6cd5cfcfda11a4e3fa7505d9e)

Build a Windows-to-POSIX/ANSI error translation layer.

Replace the read-only error mapping to WT_NOTFOUND and WT_PERM_DENIED
with EACCES and ENOENT.

Windows no longer needs its own version of __wt_strerror(), move the POSIX implementation from os_posix/os_errno.c to os_common/os_errno.c.  Rename os_win/os_errno.c to os_win/os_winerr.c to avoid a collision.

Windows now has DWORD types in prototypes, split the Windows/POSIX extern.h files. (This actually cleans up some noise, previously we had to sort the OS prototypes to remove duplicates, which wasn't trivial.)

Add the WT_EXTENSION_API.map_windows_error method to map Windows system codes to POSIX/ANSI system codes.

* WT-2541 Add stats showing active readers and writers

* Fix use of RET_MSG instead of ERR_MSG

* Change where we increment the active r/w stats

* Add "active fsync" stat

* Add new "Thread State" stat section, add fsync_io stat

* KNF

* Make thread stats not backwards breaking. Add atomic stat functions

* Add ThreadState stats to system and evict groups

* KNF

* WT-2671: dump more information about the file layout in verify debug mode

Dump the checkpoint final and correct sizes when loading checkpoints in
verify dump_XXX mode.

Dump the checkpoint alloc, discard and avail lists when loading
checkpoints in verify dump_XXX mode.

Fix a bug, convert the count of tree pages from uint32_t to uint64_t,
there's no reason pages counts can't overflow 4B.

Fix a bug, reset the internal/leaf page counts at the end of every
checkpoint, we were doing cumulative counts.

Fix a bug, where we were using "%03zu" for a size_t type, fix the
dist/s_style script to catch that case.

Add a divider line between checkpoints to make it easier to read the
output.

Add a new __wt_buf_set_size() function that displays byte values in
human-readable format.

Move __wt_buf_set_printable() from btree/bt_misc.c to support/scratch.c,
it's a general-purpose function.

Rename verify debug option from "dump_shape" to "dump_layout", we're
dumping more than the tree shape now.

* Merge the two versions of the "dump extent list" functions, and stop
dumping all of the elements, they're far too many for that to ever be
useful again. Instead, display a list by power-of-two bucket size.

* Minor changes to make bucket sizes human readable.

* block_ext.c:1477:3: error: format '%s' expects argument of type 'char *',
but argument 3 has type 'const void *' [-Werror=format]