Attempt to log distro name/version in Unix crashlog.

Factor out fork/execve/read stdout code into own function.

src/crashlog.h

@@ -44,6 +44,14 @@ protected:
 	 */
 	virtual char *LogCompiler(char *buffer, const char *last) const;
 
+	/**
+	 * Writes OS' version detail to the buffer, if available.
+	 * @param buffer The begin where to write at.
+	 * @param last   The last position in the buffer to write to.
+	 * @return the position of the \c '\0' character after the buffer.
+	 */
+	virtual char *LogOSVersionDetail(char *buffer, const char *last) const;
+
 	/**
 	 * Writes actually encountered error to the buffer.
 	 * @param buffer  The begin where to write at.