Update documentation on cache control and credential manager options
in MSI deployment guide.
'CachePath' setting in registry allows REG_EXPAND_SZ type.
Update registry documentation for 'CachePath' setting.
Both installers save the credential manager command line options in
registry.
Fix handling of existing 'afsdcell.ini' file in WiX installer.
WiX 2.0.1927 changed the XML schema. The WiX installer has beed
updated accordingly.