i3-nagbar: take our terminal execution kludge to the next level

Please read commit 2bf80528bd first.
Then read the comment within the code of this commit.
Then run in circles and cry loudly.

fixes #1002
fixes #1026

include/libi3.h

@@ -364,4 +364,12 @@ bool is_debug_build() __attribute__((const));
  */
 char *get_process_filename(const char *prefix);
 
+/**
+ * This function returns the absolute path to the executable it is running in.
+ *
+ * The implementation follows http://stackoverflow.com/a/933996/712014
+ *
+ */
+const char *get_exe_path(const char *argv0);
+
 #endif