Add experimental support for resolving relative database file paths using a fixed user-defined directory.

FossilOrigin-Name: 7354ae8fd3eccee2cf9f6501da5b1a014c31556f

src/main.c

@@ -74,6 +74,15 @@ void (*sqlite3IoTrace)(const char*, ...) = 0;
 */
 char *sqlite3_temp_directory = 0;
 
+/*
+** If the following global variable points to a string which is the
+** name of a directory, then that directory will be used to store
+** all database files specified with a relative pathname.
+**
+** See also the "PRAGMA data_store_directory" SQL command.
+*/
+char *sqlite3_data_directory = 0;
+
 /*
 ** Initialize SQLite.  
 **