Do not use mutexes in the pcache implementation unless

SQLITE_ENABLE_MEMORY_MANAGMENT is defined.  This is a performance enhancement.
A side effect is that pcaches will not steal pages from one another unless
ENABLE_MEMORY_MANAGEMENT is set, or unless SQLITE_THREADSAFE=0.

FossilOrigin-Name: e5ca59e63b18ac45a8c82ca39dc8cce1c4ce903c

diff --cc manifest
index efbad616ed5262f43f89436f17a18cdc88ddd59e,1f5d0773e52dfccc4476e6025d4c72b8240cef6e..118063a23418a871e7d400dbe603c671cf433c77
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,8 -1,8 +1,8 @@@
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- C Fix\sa\stypo\sin\sthe\sdocumentation\sfor\ssqlite3_stmt_readonly().
- D 2011-01-17T18:30:10.560
 -C Get\sall\stest\scases\sworking\swith\sthe\smutex-free-pcache\simplementation.
 -D 2011-01-18T16:13:27.224
++C Do\snot\suse\smutexes\sin\sthe\spcache\simplementation\sunless\nSQLITE_ENABLE_MEMORY_MANAGMENT\sis\sdefined.\s\sThis\sis\sa\sperformance\senhancement.\nA\sside\seffect\sis\sthat\spcaches\swill\snot\ssteal\spages\sfrom\sone\sanother\sunless\nENABLE_MEMORY_MANAGEMENT\sis\sset,\sor\sunless\sSQLITE_THREADSAFE=0.
++D 2011-01-18T17:03:26.554
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  F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
  F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
  F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
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diff --cc manifest.uuid
index 2bfaca6792304c0cd21bcaec2d6205e0e7abb7e3,f27c91d65cf88922ce3eb71c77d1e503612868d3..08777730f0c05407397a45d74e30566cd0fae8db
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 56417a3386fc84dd36bf1488e88149b1ac6a0d02
 -2dc98d29995bef51108e99aa8f7a56427cf9e1d7
++e5ca59e63b18ac45a8c82ca39dc8cce1c4ce903c