Enhance the memdb VFS so that it is able to share databases among multiple

database connections in the same process, as long as the database filename
begins with "/".  This provides a way for threads to share an in-memory
database without the use of shared-cache mode.

FossilOrigin-Name: 533fffc4a39b01c3aba75bd3271fd6ccd9516d9681ed04adbe19bd7de03f4c16

diff --cc manifest
index 465e5bc74eea2707288d5edec521a6b9c62bb3e4,e0494487e8ebb95c3e1390565a6b6a17c8efdf7e..c6bbea6614e7bb4988a5282a30941c67c421e6d8
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Fix\sa\sNEVER()\sthat\scan\ssometimes\sbe\strue.\ndbsqlfuzz\s9a86fb3830977e216fde061bfbe1c1e5c2e9bfc4
- D 2021-05-11T10:47:41.595
 -C Respond\scorrectly\sto\sOOM\sduring\smutex\sallocation.
 -D 2021-05-12T02:52:20.461
++C Enhance\sthe\smemdb\sVFS\sso\sthat\sit\sis\sable\sto\sshare\sdatabases\samong\smultiple\ndatabase\sconnections\sin\sthe\ssame\sprocess,\sas\slong\sas\sthe\sdatabase\sfilename\nbegins\swith\s"/".\s\sThis\sprovides\sa\sway\sfor\sthreads\sto\sshare\san\sin-memory\ndatabase\swithout\sthe\suse\sof\sshared-cache\smode.
++D 2021-05-12T11:55:59.991
  F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
  F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
  F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@@ -1912,7 -1912,7 +1912,8 @@@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a9
  F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
  F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
  F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
- P 6df3b03e00b1143be8fed3a39a58ce81063020275aa1ac13d87c84f1ceda6e27
- R 888429298506a7a430e45d7ff6f16cee
 -P 6c20d9d4b7c7986e8404142974a91dce7514ca574ee52ed5d036367aad396689
++P f39666e64d6d32420170c54f874d8314eb8c6f91df625f7b28f9ccffb9474dc0 98dae595d861941bb0bcd12126ee02492587c466e6da579a58b5dc4a4d655917
+ R 1441e09faa39fd11227f415ae28549ff
++T +closed 98dae595d861941bb0bcd12126ee02492587c466e6da579a58b5dc4a4d655917
  U drh
- Z 3810e14a95fb243baca7c6b1006c9619
 -Z 0e90b0427259cb6d9f6183399dca20f9
++Z bbd64c76e9984e3f1696dac12550f00b

diff --cc manifest.uuid
index d8161e31ce95a6417258555da5859ca8f9a19bb2,f1207520d2b1fab815b4c528059fabb889bf714a..6e05c7e90be4e2f883ae1d1cd95dd81bc6789741
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- f39666e64d6d32420170c54f874d8314eb8c6f91df625f7b28f9ccffb9474dc0
 -98dae595d861941bb0bcd12126ee02492587c466e6da579a58b5dc4a4d655917
++533fffc4a39b01c3aba75bd3271fd6ccd9516d9681ed04adbe19bd7de03f4c16