Add new interfaces sqlite3_value_subtype() and sqlite3_result_subtype().

Update the json1.c extension to take advantages of those interfaces to avoid
the goofy '$$' path syntax and to allow nested calls to json_array() and
json_object() that work as expected.

FossilOrigin-Name: db4152aef2253ed2a33e3cad01e0c6758e03f900

diff --cc manifest
index 69a0154d20a3e952b565072de7711d69f2bee5fd,525605fc0dfb90420ca5814f395edb6b411e58a2..3fc4b6ab33c1762e2b42fd274ada6124957670d1
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Fix\sa\spotential\sNULL\spointer\sderef\sin\sthe\stesting\slogic\sof\spcache1.\nNB:\sThe\s-DSQLITE_TEST\scompile-time\soption\sis\sneeded\sto\shit\sthe\sproblem.
- D 2015-09-10T19:22:25.531
 -C Take\sout\sthe\sgoofy\s'$$'\spath\ssyntax.\s\sInstead,\suse\ssubtypes\sto\scommunicate\swhen\na\sstring\sis\sJSON.\s\sAdd\sthe\sjson()\sfunction\sthat\svalidates\sand\sminifies\sthe\nJSON\sand\ssets\sthe\sappropriate\ssubtype.
 -D 2015-09-11T00:06:41.899
++C Add\snew\sinterfaces\ssqlite3_value_subtype()\sand\ssqlite3_result_subtype().\nUpdate\sthe\sjson1.c\sextension\sto\stake\sadvantages\sof\sthose\sinterfaces\sto\savoid\nthe\sgoofy\s'$$'\spath\ssyntax\sand\sto\sallow\snested\scalls\sto\sjson_array()\sand\njson_object()\sthat\swork\sas\sexpected.
++D 2015-09-11T00:26:04.863
  F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
  F Makefile.in f85066ce844a28b671aaeeff320921cd0ce36239
  F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@@ -1385,7 -1386,7 +1386,8 @@@ F tool/vdbe_profile.tcl 67746953071a9f8
  F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
  F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
  F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
- P 0c0c4ae971e54efc526eed7bd071c90dfadb95ff
- R 3ba34701e76f91459126301401d510a6
 -P c6fca0be11f7414292279e2ea1b004260e6f4bb6
++P f5580f08538636ffb1367e717a33756288ccddde 8a80d6459e246ec1b38325e1cbd1e862157138b3
+ R 6298ef57aadddbd507dac61cb4572ea0
++T +closed 8a80d6459e246ec1b38325e1cbd1e862157138b3
  U drh
- Z c5b1b6a1894a9ad25bccddfa15233f55
 -Z f00bae494bb0cd397ae4843df54988dc
++Z 2fd3a23a70bcc4f4e537cdb3e485fd63

diff --cc manifest.uuid
index be02be36685ca2ac0f8aa46765b67a69d55499dc,0c45a9ed674363bfeb8db71e372a55b8a7291ff0..1e2577e11502c1497d6538757a06f7205eaac135
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- f5580f08538636ffb1367e717a33756288ccddde
 -8a80d6459e246ec1b38325e1cbd1e862157138b3
++db4152aef2253ed2a33e3cad01e0c6758e03f900