[BioC] getBioC change

[Jeff Gentry]

As of the very latest version of getBioC (1.2.23) there is a small API
change that is unlikely to affect many users, but for those who it might
affect ...

Previously the version 'force' was defined as specifying if a binary
package should be installed even if the R version it was built under did
not match the current version.  The default was TRUE, such that the user
had to explicitly request this error checking.  This option is now under
the argument 'versForce', to align with the reposTools fucntions that
getBioC is calling.

Argument 'force' now also matches up with its reposTools equivalent and
specifies whether or not a package is to be downloaded and installed if
all of its dependencies are not available.  The default behaviour is that
if all of a package's dependencies are not available that the package
itself is also not downloaded and installed.  However, setting
'force=TRUE' will allow a package to be downloaded regardless.

-Jeff