Allow custom magic to be specified through --sqlite_magic (#1144)

README.md

@@ -99,6 +99,17 @@ This uses the npm_config_python config, so values in .npmrc will be honoured:
 
     python=/usr/bin/python2
 
+## Custom file header (magic)
+
+The default sqlite file header is "SQLite format 3".  
+You can specify a different magic, though this will make standard tools and libraries unable to work with your files.
+
+
+    npm install --build-from-source --sqlite_magic="MyCustomMagic15"
+
+
+Note that the magic *must* be exactly 15 characters long (16 bytes including null terminator).
+    
 ## Building for node-webkit
 
 Because of ABI differences, `sqlite3` must be built in a custom to be used with [node-webkit](https://github.com/rogerwang/node-webkit).

deps/sqlite3.gyp

 {
   'includes': [ 'common-sqlite.gypi' ],
+
+  'variables': {
+    'sqlite_magic%': '',
+  },
+
   'target_defaults': {
     'default_configuration': 'Release',
     'cflags':[
@@ -101,7 +106,14 @@
       ],
       'export_dependent_settings': [
         'action_before_build',
+      ],
+      'conditions': [
+        ["sqlite_magic != ''", {
+            'defines': [
+              'SQLITE_FILE_HEADER="<(sqlite_magic)"'
             ]
+        }]
+      ],
     }
   ]
 }