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/btree.c

@@ -1864,6 +1864,7 @@ int sqlite3BtreeOpen(
     rc = sqlite3PagerOpen(pVfs, &pBt->pPager, zFilename,
                           EXTRA_SIZE, flags, vfsFlags, pageReinit);
     if( rc==SQLITE_OK ){
+      sqlite3PagerSetMmapLimit(pBt->pPager, db->mxMmap);
       rc = sqlite3PagerReadFileheader(pBt->pPager,sizeof(zDbHeader),zDbHeader);
     }
     if( rc!=SQLITE_OK ){