Update this branch with recent checkpoint related changes from trunk.

FossilOrigin-Name: fb6b7938601505186c0b1f0df6c45630039027f85ff394d290bc2c86b16a3a07

diff --cc manifest
index 69e9a19f7ffb50017e34d396b4bff9b4ae35a55b,dea915e8ca9adc6d9a34140004617730a1daea92..22fa622242b6e42c554e48c29cb3699b2a3e42f3
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Merge\slatest\strunk\schanges\sinto\sthis\sbranch.
- D 2018-03-02T17:40:23.911
 -C In\sa\scheckpoint,\sfigure\sout\sif\sit\sis\spossible\sto\scheckpoint\sany\sframes\sat\sall\nbefore\screating\sthe\swal-iterator.
 -D 2018-03-02T16:52:47.523
++C Update\sthis\sbranch\swith\srecent\scheckpoint\srelated\schanges\sfrom\strunk.
++D 2018-03-02T17:59:37.964
  F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
  F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
  F Makefile.in a2d2fb8d17c39ab5ec52beb27850b903949080848236923f436156b72a958737
@@@ -572,8 -568,8 +572,8 @@@ F src/vdbesort.c 731a09e5cb9e96b70c394c
  F src/vdbetrace.c 48e11ebe040c6b41d146abed2602e3d00d621d7ebe4eb29b0a0f1617fd3c2f6c
  F src/vtab.c 0e4885495172e1bdf54b12cce23b395ac74ef5729031f15e1bc1e3e6b360ed1a
  F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
- F src/wal.c 44e8d9f9b42dba0dd6253d67574307ff1892ee56f3ae99cabfcec5a2676763b4
 -F src/wal.c 60e5c938c4858c72f0cb0c7220282d3066efa215ad5e82f3cf4c0b833fbe60dc
 -F src/wal.h 8de5d2d3de0956d6f6cb48c83a4012d5f227b8fe940f3a349a4b7e85ebcb492a
++F src/wal.c b6ad12df144846d02db4a18cadf9e5fcf39f1d7b7156f94131ab4076384dec07
 +F src/wal.h 1713fefe4587678c295bbeb91c4e7442998ad74f19249869ce49dda9e8ce5d53
  F src/walker.c da987a20d40145c0a03c07d8fefcb2ed363becc7680d0500d9c79915591f5b1f
  F src/where.c 7cae47e813393d70c6d327fdf000fcb30f76b1b0b5a5b52ff6402e0c658de32c
  F src/whereInt.h 82c04c5075308abbac59180c8bad5ecb45b07453981f60a53f3c7dee21e1e971
@@@ -1719,7 -1708,7 +1719,7 @@@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a9
  F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
  F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
  F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
- P 163c870950f386f6b0bb1ff9b3886cf95ba0deed414cae75baf87621ed3528c2 1293d4f64f322ee57510bdff497c54e0be2c9205217e1fd96887bba1f36bec40
- R d95135aa69ebdf39b1d9aaa7d36a2c84
 -P 0f5057dffa9be1bccab04894709d25bf1f066c4b1aef50d67ee635d46d300a4d
 -R de1a2fcd17a7874df266511eaa97ccfc
++P 36801effa9ec67b551f58972e21794466420f10cd0420701fcd87695e6cd11ee 044b0b65e716bffeddedbd1b0360c4c332f6d2359167c1d327a5ff96539474cb
++R db5621b69ea924f8256c1ea108391b00
  U dan
- Z 069d19cd10e378f6784afc839a1c9bac
 -Z 77af2128f3c4feb420234b4cd2eef89e
++Z 5f73e55771155cb4923ea7c8cff8af6b

diff --cc manifest.uuid
index 5638c6d4d4e2cc9fdfbe230ad8c6762224de2026,4f3871ee750df94bde628b93dd813249358fde89..fc240c969cb563cbd57e8071515cc320ecfeb0b2
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 36801effa9ec67b551f58972e21794466420f10cd0420701fcd87695e6cd11ee
 -044b0b65e716bffeddedbd1b0360c4c332f6d2359167c1d327a5ff96539474cb
++fb6b7938601505186c0b1f0df6c45630039027f85ff394d290bc2c86b16a3a07

diff --cc src/wal.c
Simple merge