Handle upgrades of packages within ranges

The underlying functionality for this was already present within
`pip-tool`s, however `pip-compile-multi` wasn't aware of it and
thus made assumptions about the nature of the spec argument which
turned out to be false.

The fix here is to teach `pip-compile-multi` how to interpret these
package specs to extract the names for the places it needs them
while still passing the full spaces through to `pip-tools` for the
actual upgrade.

Fixes peterdemin#392

pipcompilemulti/features/upgrade.py

@@ -33,6 +33,8 @@
         https://github.com/jazzband/pip-tools#updating-requirements
 """
 
+import re
+
 from .base import BaseFeature, ClickOption
 from .forward import ForwardOption
 
@@ -78,10 +80,19 @@ def reset(self):
         """Clear cached packages."""
         self._env_packages_cache = {}
 
+    @property
+    def package_specs(self):
+        """List of package specs to upgrade."""
+        return self.value or []
+
     @property
     def package_names(self):
         """List of package names to upgrade."""
-        return self.value or []
+        def name_from_spec(name):
+            match = re.match(r'(?P<package>[a-z0-9-_.]+)', name)
+            assert match is not None
+            return match.group(0)
+        return [name_from_spec(x) for x in self.package_specs]
 
     @property
     def active(self):
@@ -92,7 +103,7 @@ def pin_options(self):
         """Pin command options for upgrading specific packages."""
         return [
             '--upgrade-package=' + package
-            for package in self.package_names
+            for package in self.package_specs
         ]
 
     def has_package(self, in_path, package_name):