Configury updates for verbs, sockets, psm

Per prior discussion, now that #112 has been merged, I added a round of provider configury updates:

* Split the provider-specific configury into their own .m4 files
* Separate updates for the configury for each of the verbs, sockets, and psm providers

Note that I deleted the confusing (IMHO) --enable-psm, --with-psm, --with-psm-include, and --with-psm-lib switches.  There's only --enable-psm now, and you can specify a prefix to it, if you want.  For example:

```sh
$ ./configure --enable-psm=/path/to/psm-install-tree
```

Note that specifying a directory is somewhat a convenience for specifying CPPFLAGS/LDFLAGS on the command line.  For example, if you want to build PSM as a DSO, you need to:

```sh
$ ./configure CPPFLAGS=-I/path/to/psm/include LDFLAGS=-L/path/to/psm/lib --enable-psm=dl
```

That being said, I do not have libpsm_infinipath, so I can't test that particular configury.