Add Perl support for ucalls / uflow / ustat (#1959)

Sort language entries while at it.
diff --git a/tools/lib/ucalls_example.txt b/tools/lib/ucalls_example.txt
index fffc76f..69d401a 100644
--- a/tools/lib/ucalls_example.txt
+++ b/tools/lib/ucalls_example.txt
@@ -2,8 +2,9 @@
 
 
 ucalls summarizes method calls in various high-level languages, including Java,
-Python, Ruby, PHP, and Linux system calls. It displays statistics on the most 
-frequently called methods, as well as the latency (duration) of these methods.
+Perl, PHP, Python, Ruby, and Linux system calls. It displays statistics on the
+most frequently called methods, as well as the latency (duration) of these
+methods.
 
 Through the syscalls support, ucalls can provide basic information on a 
 process' interaction with the system including syscall counts and latencies. 
@@ -60,7 +61,7 @@
 USAGE message:
 
 # ./ucalls.py -h
-usage: ucalls.py [-h] [-l {java,python,ruby,php,none}] [-T TOP] [-L] [-S] [-v]
+usage: ucalls.py [-h] [-l {java,perl,php,python,ruby,none}] [-T TOP] [-L] [-S] [-v]
                  [-m]
                  pid [interval]
 
@@ -72,7 +73,7 @@
 
 optional arguments:
   -h, --help            show this help message and exit
-  -l {java,python,ruby,php,none}, --language {java,python,ruby,php,none}
+  -l {java,perl,php,python,ruby,none}, --language {java,perl,php,python,ruby,none}
                         language to trace (if none, trace syscalls only)
   -T TOP, --top TOP     number of most frequent/slow calls to print
   -L, --latency         record method latency from enter to exit (except