Rcmd install mypkg

Requiring Perl script names to be specified in a case-sensitive way
doesn't affect the R build process, but it does mean that a script
written on Windows is slightly more likely to work when someone runs it
on another platform.  There's an "install" command in at least some
flavours of Unix that would be invoked instead of R's INSTALL script if
you said "R CMD install" on one of those platforms, and that's not a
good thing.