update changelog for 1.21.12

CHANGELOG.txt

@@ -1,18 +1,32 @@
-XXXX-YY-ZZ 1.21.x:
+2016-08-17 1.21.12:
 ------------------
 
 Enhancements:
 -------------
 
 * Whitelist the CPU_COUNT environment variable. #1149
+* Add tool for examining prefix length in existing packages #1195
+* Add a conda interface layer for better compatibility with conda 4.2 #1200 #1203 #1206
+* Document how to run tests #1205
+* Update default versions for R (3.3.1) and Perl (5.20.3) builds #1220
+
 
 Bug fixes:
 ----------
 
+* Don't compile .py files in executable locations.  Compile one at a time.  #1186
+* Don't force download if vcs is used as a source #1212
+* Break hardlinks as a post-install step.  Hard links can cause problems at package install time.  #1215
+* Make environment variables used by conda in environment creation always be bytestrings #1216 #1219
+
+
 Contributors:
 -------------
 
 * @jakirkham
+* @kalefranz
+* @msarahan
+
 
 2016-08-06 1.21.11:
 -------------------