perf annotate: Print the evsel name in the stdio output

So that when showing multiple events annotations, we can figure out
which is which:

# perf record -a -e instructions,cycles sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.826 MB perf.data (~36078 samples) ]
# perf evlist
instructions
cycles
# perf annotate intel_idle 2> /dev/null | head -1
Percent | Source code & Disassembly of vmlinux for instructions
#

Cc: Adrian Hunter <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/annotate.c

···
 	struct dso *dso = map->dso;
 	char *filename;
 	const char *d_filename;
+	const char *evsel_name = perf_evsel__name(evsel);
 	struct annotation *notes = symbol__annotation(sym);
 	struct disasm_line *pos, *queue = NULL;
 	u64 start = map__rip_2objdump(map, sym->start);
···
 	int more = 0;
 	u64 len;
 	int width = 8;
-	int namelen;
+	int namelen, evsel_name_len, graph_dotted_len;
 
 	filename = strdup(dso->long_name);
 	if (!filename)
···
 
 	len = symbol__size(sym);
 	namelen = strlen(d_filename);
+	evsel_name_len = strlen(evsel_name);
 
 	if (perf_evsel__is_group_event(evsel))
 		width *= evsel->nr_members;
 
-	printf(" %-*.*s|	Source code & Disassembly of %s\n",
-	       width, width, "Percent", d_filename);
-	printf("-%-*.*s-------------------------------------\n",
-	       width+namelen, width+namelen, graph_dotted_line);
+	printf(" %-*.*s|	Source code & Disassembly of %s for %s\n",
+	       width, width, "Percent", d_filename, evsel_name);
+
+	graph_dotted_len = width + namelen + evsel_name_len;
+	printf("-%-*.*s-----------------------------------------\n",
+	       graph_dotted_len, graph_dotted_len, graph_dotted_line);
 
 	if (verbose)
 		symbol__annotate_hits(sym, evsel);