CoxeterGroup / coxeter3 trouble

edit

I'm having some trouble using the optional coxeter3 package - can somebody see what I'm doing wrong?

I just built a clean version of sage 8.0, freshly cloned from github, on my ubuntu machine. Then I ran

sage -i coxeter3

as one does; it installed with no errors. It seems to have worked: installed_packages(), for instance, has the line

 'coxeter3': '1.1',

and there's a sage.libs.coxeter3 module in the namespace. But, for instance, when I try to use coxeter3 as per the instructions on the Coxeter Groups page in the sage documentation (can't provide a link as karma is too low), I get a RuntimeError:

   sage: W = CoxeterGroup(["A",2], implementation='coxeter3')
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-12-4f0efd988562> in <module>()
----> 1 W = CoxeterGroup(["A",Integer(2)], implementation='coxeter3')

/home/bjy/build/sage/local/lib/python2.7/site-packages/sage/combinat/root_system/coxeter_group.pyc in CoxeterGroup(data, implementation, base_ring, index_set)
    142             from sage.libs.coxeter3.coxeter_group import CoxeterGroup
    143         except ImportError:
--> 144             raise RuntimeError("coxeter3 must be installed")
    145         else:
    146             return CoxeterGroup(cartan_type)

RuntimeError: coxeter3 must be installed

Any help is appreciated! I don't know enough even to start troubleshooting, though I tried the usual kinds of google searches and such.

===============

Updates: 'coxeter3' ISN'T in dir(sage.libs) for me, so it looks like the package didn't "fully install", or something. It's entirely possible that I didn't install the package correctly; I still haven't managed to find a clear set of intallation instructions. I did try doing "make build" after 'sage -i coxeter3" as per FrédéricC's comment; my computer churned away for a while, but ultimately it didn't change anything.

Maybe I can more precisely target my question. Where can I find a clear set of instructions for how to install the optional Coxeter3 spkg in a current sage build?

================

Update 2: So, apparently the ting to do is to say

sage -f Coxeter3 
sage -b

whereupon everything works - except that dir(sage.libs) still has no mention of Coxeter3, so I'm not sure what's up with that.

For those following along at home: as far as I can see, the first command causes Coxeter3 to be forcefully reinstalled, regardless of what I did beforehand to mess things up; presumably the "-b" in the second command is "build" in some capacity.

Thanks folks!