Merge change to drop the mutex on the multiplexor before entering the xRead

VFS call, in order to enhance parallelizability.

FossilOrigin-Name: 3c566e41e4c9c66960cc5a3ddee8556835237999

diff --cc manifest
index 9c88c23de6c1fc8822ae1346804f1366d0513142,02b5ae33a8674d73c1ec64085cd687862a26a064..be690b076640598aa72ce825d0fc6dfcf12d37d8
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,12 -1,12 +1,12 @@@
- C Optimize\sout\sa\sNotExists/NotFound\sopcode\sthat\soccurs\sin\sUPDATE\sprocessing\nafter\sconstraint\schecks\sif\sthere\sis\sno\spossiblity\sthat\sthe\sconstraint\schecking\ncode\smight\shave\smoved\sthe\scursor.
- D 2013-11-08T01:09:15.717
 -C Drop\sthe\smutex\son\sthe\smultiplexor\sbefore\sentering\sthe\sxRead\sVFS\scall.
 -D 2013-10-21T13:15:55.814
++C Merge\schange\sto\sdrop\sthe\smutex\son\sthe\smultiplexor\sbefore\sentering\sthe\sxRead\nVFS\scall,\sin\sorder\sto\senhance\sparallelizability.
++D 2013-11-08T12:14:50.705
  F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 -F Makefile.in 0522b53cdc1fcfc18f3a98e0246add129136c654
 +F Makefile.in d12e4455cf7a36e42d3949876c1c3b88ff70867a
  F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
 -F Makefile.msc ec5d662ed5a15ff819928c0495017af13910d7b6
 +F Makefile.msc eaf39e18f37637111c6e39ed35b1da9092c8816f
  F Makefile.vxworks db21ed42a01d5740e656b16f92cb5d8d5e5dd315
  F README cd04a36fbc7ea56932a4052d7d0b7f09f27c33d6
 -F VERSION a8d1f6839521130dc73c5408cdd24bcfd791df34
 +F VERSION 52f7e22bfcec71a462e34194b4ae1671380fde59
  F aclocal.m4 a5c22d164aff7ed549d53a90fa56d56955281f50
  F addopcodes.awk 17dc593f791f874d2c23a0f9360850ded0286531
  F art/sqlite370.eps aa97a671332b432a54e1d74ff5e8775be34200c2
@@@ -1135,7 -1126,10 +1135,8 @@@ F tool/vdbe-compress.tcl f12c884766bd14
  F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
  F tool/warnings.sh d1a6de74685f360ab718efda6265994b99bbea01
  F tool/win/sqlite.vsix 030f3eeaf2cb811a3692ab9c14d021a75ce41fff
- P 1d1d13b89056903543c909b094030d205473fa82
- R a93c908485a9c317c37cb2c75e7c2fa6
 -P 4bd592c8f0e011e203443a6e88008a61d6926df5
 -R 1b819a89ed2e2eb5d84ea2573089e8d1
 -T *branch * multiplex-parallel-read
 -T *sym-multiplex-parallel-read *
 -T -sym-trunk *
++P 74e3ee2ee6ea89af2c12dd0bce248467fd0f1310 a00d2ed49c9f53263cd76ad41dad9e35e646ebb5
++R 3835fd3c0df78c22220952d9100c6a09
++T +closed a00d2ed49c9f53263cd76ad41dad9e35e646ebb5
  U drh
- Z 8c016c61c4a5769a5b69311c7541f889
 -Z 4ddaa29dcb59ed6dc8dd87737e60aeca
++Z 74a2387ae02d248fbf85568c38a09fbd

diff --cc manifest.uuid
index d7d315200cfe01328aab8b8b347c7146f9cff6ff,37e946f48c79797a76f19fdd717a60708af63f3a..5bc804df30aa79f6e458912573a7afbf4b18705c
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 74e3ee2ee6ea89af2c12dd0bce248467fd0f1310
 -a00d2ed49c9f53263cd76ad41dad9e35e646ebb5
++3c566e41e4c9c66960cc5a3ddee8556835237999