Spelling error and bad web link

The file src/gui/dialogs/qmessagebox.cpp has a couple of spelling errors and a web link that is no longer valid:

This is the approach recommended in the
\l

{http://developer.apple.com/documentation/UserExperience/Conceptual/AppleHIGuidelines/XHIGWindows/chapter_18_section_7.html}

{Mac OS X Guidlines}

. Similar guidlines apply for the other
platforms, but note the different ways the
\l

{QMessageBox::informativeText}

{informative text}

is handled for
different platforms.

"Guidlines" and "guidlines" are misspelled. The Apple.com web link is no longer valid.