boost: fix build with uClibc, add locale/timer modules options

Boost 1.49 added two new modules, locale and timer - So add sub options
to control compilation of those. The locale module by default compiles
the posix backend under Linux, but this needs monetary.h which isn't
provided by uClibc, so work around that.

While we're at it, hide the icu option as that is just an internal
configuration option used by E.G. the locale module.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>