Fix an issue with a stray glyph in the window title bar.
    
    The ASCII DEL (127) character was appended to the end of every title bar.
    
    This patch fixes the issue by properly assigning PRE_RELEASE_SUFFIX
    to an empty string rather than a literal "".  The literal double-quotes
    were getting defined to the preprocessor as -DPRE_RELEASE_SUFFIX=""""
    and after preprocessing, browser.xul had ASCII DEL (127) characters
    instead of the empty string.