Keep non-significant blanks node in HTML parser

For https://bugzilla.gnome.org/show_bug.cgi?id=681822

Regardless if the option HTML_PARSE_NOBLANKS is set or not, blank nodes
are removed from a HTML document, for example:

<html>
  <head>
    <title>This is a test.</title>
  </head>
  <body>
    <p>This is a test.</p>
  </body>
</html>

is read as:

<html><head><title>This is a test.</title></head><body>
    <p>This is a test.</p>
  </body></html>

This changes the default behaviour but the old behaviour is available
as expected when using the parser flag HTML_PARSE_NOBLANKS

Based on original patch from Igor Ignatyuk <igor_ignatiouk@hotmail.com>

* HTMLparser.c: change various places in the parser where ignorable_space
  SAX callback was called without checking for the parser flag preference
* xmllint.c: make sure we use the new flag even for HTML parsing
* result/HTML/*: this modifies the output of a number of tests
diff --git a/result/HTML/53867.html b/result/HTML/53867.html
index acdad7c..f4902af 100644
--- a/result/HTML/53867.html
+++ b/result/HTML/53867.html
@@ -1,5 +1,7 @@
 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
-<html><head><style>
+<html>
+<head>
+<style>
 .......
 ...............................................................
 ...............................................................
@@ -63,4 +65,6 @@
 ...............................................................
 ...............................................................
 ...............................................................
-</style></head></html>
+</style>
+</head>
+</html>