Added support for asset loading on Android.

Requires passing the activity's AssetManager object from Java to GNUstep by calling +[NSBundle setJavaAssetManager:withJNIEnv:], which then enables the following features:

- NSBundle main bundle resource paths support for Android assets, e.g. for pathForResource:ofType:, URLForResource:ofType: and related methods.
- NSBundle main bundle info dictionary support if Info.plist exists in Android assets.
- -initWithContentsOfFile: and related methods support for reading Android assets from main bundle in various classes (e.g. NSData, NSDictionary, NSArray, etc.).
- NSFileManager fileExistsAtPath:(isDirectory:) and isReadableFileAtPath: return YES for main bundle asset / asset directory paths.
- NSFileHandle support for reading Android assets from main bundle.
- NSDirectoryEnumerator support for enumerating Android assets from main bundle. Note that recursion into subdirectories is currently not supported by the native Android asset manager API (see https://issuetracker.google.com/issues/37002833).

Also adds support for automatic NSProcessInfo initialization on Android with a fake executable path "/data/data/<app identifier>/exe" (as Android apps don't have a real executable path), and tweaks main bundle initialization to allow that path. Main bundle resource paths are prefixed by "/data/data/<app identifier>/Resources".

Source/NSProcessInfo.m

@@ -943,6 +943,31 @@ extern char **__libc_argv;
     }
 }
 
+#elif defined(__ANDROID__)
+
++ (void) initialize
+{
+  if (nil == procLock) procLock = [NSRecursiveLock new];
+  if (self == [NSProcessInfo class]
+    && !_gnu_processName && !_gnu_arguments && !_gnu_environment)
+    {
+      FILE *f = fopen("/proc/self/cmdline", "r");
+      if (f) {
+        char identifier[BUFSIZ];
+        fgets(identifier, sizeof(identifier), f);
+        fclose(f);
+        
+        // construct fake executable path
+        char *arg0;
+        asprintf(&arg0, "/data/data/%s/exe", identifier);
+
+        char *argv[] = { arg0 };
+        _gnu_process_args(sizeof(argv)/sizeof(char *), argv, NULL);
+      } else {
+        fprintf(stderr, "Failed to read cmdline\n");
+      }
+    }
+}
 
 #else
 + (void) initialize