Initial implementation of file-nr

Fixed file-nr update function

Fixed file-nr test case

Fixed file-nr test case again

Fixed file-nr separator to tab

Updated file-nr to filenr.

Updated file-nr to filenr.

Fixed file-nr test cases, added comments

Remove reporting the second value from file-nr as it will alwasy be zero in linux 2.6 and greator

Renaming file-nr to filefd

Updated build constraint

Updates and code cleanup for filefd.

Updated enabledCollectors with the correct name for filefd

Fixed filefd test wording

collector/filefd_linux_test.go

@@ -0,0 +1,27 @@
+package collector
+
+import (
+	"os"
+	"testing"
+)
+
+func TestFileFDStats(t *testing.T) {
+	file, err := os.Open("fixtures/file-nr")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+
+	fileFDStats, err := parseFileFDStats(file, fileName)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if want, got := "1024", fileFDStats["allocated"]; want != got {
+		t.Errorf("want filefd allocated %s, got %s", want, got)
+	}
+
+	if want, got := "1631329", fileFDStats["maximum"]; want != got {
+		t.Errorf("want filefd maximum %s, got %s", want, got)
+	}
+}