Make the unix VFS defensive against the error of having a database file open

on file descriptors 1 or 2, as an error message might easily be written onto
those file descriptors and thus overwrite and corrupt the database.

FossilOrigin-Name: 30d38cc44904d93508b87e373b2f45d5f93e556b

diff --cc manifest
index 86dc44c7b979c6cb2b0fa2d99e2834e9a1ccf054,de5d40e963e43250adff910e3b5bf7892432a6e3..aba50366ba51d0deb33b87dcf449c4ec5c825937
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Restore\sfix\s[f15591f802],\swhich\swas\saccidentally\sclobbered\sby\sthe\sstat4\smerge.
- D 2013-08-29T14:56:14.988
 -C Change\sthe\sunix\sVFS\sso\sthat\sit\srefuses\sto\sopen\sa\sdatabase\sfile\susing\na\sfile\sdescriptor\sless\sthan\s3.
 -D 2013-08-29T23:34:53.402
++C Make\sthe\sunix\sVFS\sdefensive\sagainst\sthe\serror\sof\shaving\sa\sdatabase\sfile\sopen\non\sfile\sdescriptors\s1\sor\s2,\sas\san\serror\smessage\smight\seasily\sbe\swritten\sonto\nthose\sfile\sdescriptors\sand\sthus\soverwrite\sand\scorrupt\sthe\sdatabase.
++D 2013-08-29T23:36:49.784
  F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
  F Makefile.in 5e41da95d92656a5004b03d3576e8b226858a28e
  F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@@ -1109,7 -1109,7 +1109,7 @@@ F tool/warnings-clang.sh f6aa929dc20ef1
  F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
  F tool/wherecosttest.c f407dc4c79786982a475261866a161cd007947ae
  F tool/win/sqlite.vsix 97894c2790eda7b5bce3cc79cb2a8ec2fde9b3ac
- P c1152bdcbb5ac185f743015fff63769effa81b4b
- R ef3cf6caed80e05bf3e44c08e4ed05a0
- U dan
- Z a6b4620a23effa55e7cb7c1762a8f7ee
 -P 3426673e4659eb68dbd14a3e41d4620d748432db
++P d4b6ad3333cc3bad500c2ebf7a6ea552b6762b69 66dddda06898abbf97fe0ac6a10ce1527ca8605e
+ R fe0bcec8f0ab9128b1355459470b05e0
+ U drh
 -Z 4edcc0d4a963da6c4b3d4505d80b9383
++Z 9dc425ab0a1c3ed5b98a1a49ce3d4048

diff --cc manifest.uuid
index 9346487f5cf700678d7f7a5687069b41ade8b2bd,92e6bed271847b5d5b1dbac3e6d67d2de815d535..d0b72f40908f8cea3c5c59eae36a5f5ded713580
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- d4b6ad3333cc3bad500c2ebf7a6ea552b6762b69
 -66dddda06898abbf97fe0ac6a10ce1527ca8605e
++30d38cc44904d93508b87e373b2f45d5f93e556b