Add the SQLITE_CONFIG_MMAP_LIMIT configuration option for overriding the

SQLITE_DEFAULT_MMAP_LIMIT compile-time setting.  Enhance "PRAGMA mmap_limit"
so that without a specific database name, it sets the limit on all database
files and changes the default for any future databases that might be added
using ATTACH.

FossilOrigin-Name: 78141d0a16dd1d56b575fccd149de7fa789cb06c

src/global.c

@@ -156,6 +156,7 @@ SQLITE_WSD struct Sqlite3Config sqlite3Config = {
    (void*)0,                  /* pHeap */
    0,                         /* nHeap */
    0, 0,                      /* mnHeap, mxHeap */
+   SQLITE_DEFAULT_MMAP_LIMIT, /* mxMmap */                       
    (void*)0,                  /* pScratch */
    0,                         /* szScratch */
    0,                         /* nScratch */