Document Path.is_mount(), update Misc/ACKS and Misc/NEWS (#2980)

diff --git a/Misc/ACKS b/Misc/ACKS
index e0640c1..f1f6c14 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -886,6 +886,7 @@
 James Lee
 John J. Lee
 Thomas Lee
+Cooper Ry Lees
 Tennessee Leeuwenburg
 Luc Lefebvre
 Pierre Paul Lefebvre
diff --git a/Misc/NEWS.d/next/Library/2017-08-01-15-56-50.bpo-30897.OuT1-Y.rst b/Misc/NEWS.d/next/Library/2017-08-01-15-56-50.bpo-30897.OuT1-Y.rst
new file mode 100644
index 0000000..41a75b8
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-08-01-15-56-50.bpo-30897.OuT1-Y.rst
@@ -0,0 +1,3 @@
+``pathlib.Path`` objects now include an ``is_mount()`` method (only
+implemented on POSIX).  This is similar to ``os.path.ismount(p)``. Patch by
+Cooper Ry Lees.