Add huge page configuration and pages_[no}huge().

Add the --with-lg-hugepage configure option, but automatically configure
LG_HUGEPAGE even if it isn't specified.

Add the pages_[no]huge() functions, which toggle huge page state via
madvise(..., MADV_[NO]HUGEPAGE) calls.

test/unit/pages.c

@@ -0,0 +1,30 @@
+#include "test/jemalloc_test.h"
+
+TEST_BEGIN(test_pages_huge)
+{
+	size_t alloc_size;
+	bool commit;
+	void *pages, *hugepage;
+
+	alloc_size = HUGEPAGE * 2 - PAGE;
+	commit = true;
+	pages = pages_map(NULL, alloc_size, &commit);
+	assert_ptr_not_null(pages, "Unexpected pages_map() error");
+
+	hugepage = (void *)(ALIGNMENT_CEILING((uintptr_t)pages, HUGEPAGE));
+	assert_b_ne(pages_huge(hugepage, HUGEPAGE), have_thp,
+	    "Unexpected pages_huge() result");
+	assert_false(pages_nohuge(hugepage, HUGEPAGE),
+	    "Unexpected pages_nohuge() result");
+
+	pages_unmap(pages, alloc_size);
+}
+TEST_END
+
+int
+main(void)
+{
+
+	return (test(
+	    test_pages_huge));
+}