Ignore dependencies, which have become part of stdlib

To avoid confusing error messages about unavailable dependencies, ignore those
which are known to have been becoming part of python's standard library.

At the moment that's "pathlib" and "typing" for python 3.8

package_control/library.py

@@ -7,6 +7,12 @@
 from . import distinfo
 from .clear_directory import delete_directory
 
+# 3rd-party libraries, which are part of stdlib as of certain python version
+BUILTIN_38_LIBRARIES = {
+    "3.3": {},
+    "3.8": {"pathlib", "typing"}
+}
+
 # Most legacy dependency are simply re-packed python packages.
 # Some of them had been given different names, which would cause issues, when
 # installing them directly from pypi.org. They are therefore translated, using
@@ -25,6 +31,19 @@
 }
 
 
+def builtin_libraries(python_version):
+    """
+    Determine built-in library names, which were 3rd-party libraries before
+
+    :param python_version:
+        The python version to return built-in libraries for
+
+    :returns:
+        A set of library names.
+    """
+    return BUILTIN_38_LIBRARIES.get(python_version, set())
+
+
 def translate_name(dependency_name):
     """
     Translate old dependency name to real pypi library name

package_control/package_manager.py

@@ -237,7 +237,13 @@ def get_libraries(self, package_name):
         if not names:
             return set()
 
-        return set(library.Library(library.translate_name(name), python_version) for name in names)
+        builtin = library.builtin_libraries(python_version)
+
+        return set(
+            library.Library(library.translate_name(name), python_version)
+            for name in names
+            if name not in builtin
+        )
 
     def get_python_version(self, package_name):
         """
@@ -1230,8 +1236,13 @@ def install_library(self, lib):
                 library_names = self.select_libraries(lib_info)
 
             if library_names:
+                builtin = library.builtin_libraries(lib.python_version)
                 self.install_libraries(
-                    (library.Library(library.translate_name(name), lib.python_version) for name in library_names),
+                    (
+                        library.Library(library.translate_name(name), lib.python_version)
+                        for name in library_names
+                        if name not in builtin
+                    ),
                     fail_early=False
                 )
 
@@ -1567,8 +1578,13 @@ def install_package(self, package_name, unattended=False):
                 library_names = self.select_libraries(lib_info)
 
             if library_names:
+                builtin = library.builtin_libraries(python_version)
                 self.install_libraries(
-                    (library.Library(library.translate_name(name), python_version) for name in library_names),
+                    (
+                        library.Library(library.translate_name(name), python_version)
+                        for name in library_names
+                        if name not in builtin
+                    ),
                     fail_early=False
                 )