Fix typos.

docs/usermanual-clusters.xml

@@ -290,11 +290,11 @@
   0 ,3,2,4   
 </programlisting>
     <para>
-      There's no way to differentitate between these two scenarios based
+      There's no way to differentiate between these two scenarios based
       on the cluster numbers alone.
     </para>
     <para>
-      Another problem appens with ligatures under level 2 if the
+      Another problem happens with ligatures under level 2 if the
       direction of the text is forced to opposite of its natural
       direction (e.g. left-to-right Arabic). But that's too much of a
       corner case to worry about.

docs/usermanual-install-harfbuzz.xml

@@ -50,7 +50,7 @@
       and hb-shape under <filename>util/</filename>.
     </para>
     <para>
-      If you are bootstraping from git, you need a few more tools before you
+      If you are bootstrapping from git, you need a few more tools before you
       can run <filename>autogen.sh</filename> for the first time. Namely,
       pkg-config and <ulink url="http://www.complang.org/ragel/">ragel</ulink>.
       Again, on Ubuntu / Debian:

src/hb-font.h

@@ -456,7 +456,7 @@ hb_font_get_glyph_from_name (hb_font_t *font,
 /* high-level funcs, with fallback */
 
 /* Calls either hb_font_get_nominal_glyph() if variation_selector is 0,
- * otherwise callse hb_font_get_variation_glyph(). */
+ * otherwise calls hb_font_get_variation_glyph(). */
 HB_EXTERN hb_bool_t
 hb_font_get_glyph (hb_font_t *font,
 		   hb_codepoint_t unicode, hb_codepoint_t variation_selector,