Make the c and ac scripts work with sh and without bin in PATH

Make the bin/c and bin/ac scripts work with sh. The scripts are run with
/bin/sh shebang, which fails atleast on ubuntu 12.04 /bin/sh. The sh in
Ubuntu 12.04 is dash.

The fixes are according to the suggestions in http://mywiki.wooledge.org/Bashism

Also run "compare" script with explicit ./bin/ path to support people
who do not have skia/bin in PATH.

Review URL: https://codereview.chromium.org/1139033005
diff --git a/bin/ac b/bin/ac
index 05fd605..30e9534 100755
--- a/bin/ac
+++ b/bin/ac
@@ -6,7 +6,7 @@
 CLEAN=${CLEAN-clean}
 SAMPLES=100
 
-if [ $BRANCH == $CLEAN ]; then
+if [ "$BRANCH" = "$CLEAN" ]; then
     echo "Comparing $BRANCH to itself."
     exit 1
 fi
@@ -23,4 +23,4 @@
 platform_tools/android/bin/android_ninja -t Release nanobench
 platform_tools/android/bin/android_run_skia -t Release nanobench $@ --skps /data/local/tmp/skps -i /data/local/tmp/resources --samples $SAMPLES -v > $BRANCH.log
 
-compare $CLEAN.log $BRANCH.log
+./bin/compare $CLEAN.log $BRANCH.log
diff --git a/bin/c b/bin/c
index 129a4e1..6e3bd6e 100755
--- a/bin/c
+++ b/bin/c
@@ -6,7 +6,7 @@
 CLEAN=${CLEAN-clean}
 SAMPLES=100
 
-if [ $BRANCH == $CLEAN ]; then
+if [ "$BRANCH" = "$CLEAN" ]; then
     echo "Comparing $BRANCH to itself."
     exit 1
 fi
@@ -23,4 +23,4 @@
 ninja -C out/Release nanobench
 out/Release/nanobench $@ --samples $SAMPLES -v 2> $BRANCH.log
 
-compare $CLEAN.log $BRANCH.log
+./bin/compare $CLEAN.log $BRANCH.log