Enhance the pcache1 page cache so that it tries to allocate a block of

SQLITE_DEFAULT_PCACHE_INITSZ pages from malloc() on startup, and uses those
preallocated pages when possible rather than going to malloc() for each
individual page.  About a 5% performance increase for some workloads.

FossilOrigin-Name: 5348ffc3fda5168c1e9e14aa88b0c6aedbda7c94

diff --cc manifest
index b76060a668b702a6feb98664b9425db8e91c3f8f,4fa0ddf103f4e469b914a5228f2127a116d55ab6..8742d04df9ada7b08af04ebdb7e8976ee23304fe
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Early\sdetection\sof\sfile\scorruption\sin\sa\sdebugging\sroutine,\sbefore\sthe\sinvalid\ndata\scan\scause\sproblems.
- D 2015-07-08T12:25:38.106
 -C Comment\sfix.\s\sNo\schanges\sto\scode.
 -D 2015-07-08T14:13:44.573
++C Enhance\sthe\spcache1\spage\scache\sso\sthat\sit\stries\sto\sallocate\sa\sblock\sof\nSQLITE_DEFAULT_PCACHE_INITSZ\spages\sfrom\smalloc()\son\sstartup,\sand\suses\sthose\npreallocated\spages\swhen\spossible\srather\sthan\sgoing\sto\smalloc()\sfor\seach\nindividual\spage.\s\sAbout\sa\s5%\sperformance\sincrease\sfor\ssome\sworkloads.
++D 2015-07-08T16:22:42.453
  F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
  F Makefile.in 017bf0511d1b2dd1db5e16488fbf75a17b526cbc
  F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@@ -1364,7 -1364,7 +1364,8 @@@ F tool/vdbe_profile.tcl 67746953071a9f8
  F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
  F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
  F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
- P 6ace73541ae48aeb19e0c2d9f6772d032d0a7eae
- R 8adde983bcb4c45839c171b768ffd3b9
 -P 75d98dae676996a05e97b09b19e34463e8f30d51
 -R e0f37cdeba600c01a32ef205d5f6df52
++P b27a47fef995f0ab2516e6ca779711cab1f50fb9 c1e2ed0ef4d3436d19d3203c5fb553caac53659e
++R 0716d0744f0e72c8cdadbca41133bc14
++T +closed c1e2ed0ef4d3436d19d3203c5fb553caac53659e
  U drh
- Z b9cf714cb314f182c61af66a54b1bb68
 -Z cb924bafedede368f45cad3c12c2aa68
++Z eea1350426d30f63377f69d37a46ee1a

diff --cc manifest.uuid
index 9b6013994f76561d7368ce36017b6ed8e14046e7,fb850df2b9931c8959995c9ef1e0d8c415b5191b..a2762d1d63c1e874d1b829ca2740090d33a2f207
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- b27a47fef995f0ab2516e6ca779711cab1f50fb9
 -c1e2ed0ef4d3436d19d3203c5fb553caac53659e
++5348ffc3fda5168c1e9e14aa88b0c6aedbda7c94