Consolidate the glob case logic

Looking at the code as a whole, we ended up with a little to much "buttons". It turns out that doing case insensitive matching (lower both pattern and strings to match) performs just fine. Or at least, it
gives the penalty to the people who uses mixed case filenames.

```
GetGlob/Default_cache-10                          10.6ns ± 2%    10.6ns ± 1%   ~     (p=0.657 n=4+4)
GetGlob/Filenames_cache,_lowercase_searchs-10     10.6ns ± 2%    10.6ns ± 0%   ~     (p=1.000 n=4+4)
GetGlob/Filenames_cache,_mixed_case_searchs-10    29.7ns ± 1%    29.6ns ± 1%   ~     (p=0.886 n=4+4)
GetGlob/GetGlob-10                                13.7ns ± 1%    13.7ns ± 0%   ~     (p=0.429 n=4+4)

name                                            old alloc/op   new alloc/op   delta
GetGlob/Default_cache-10                           0.00B          0.00B        ~     (all equal)
GetGlob/Filenames_cache,_lowercase_searchs-10      0.00B          0.00B        ~     (all equal)
GetGlob/Filenames_cache,_mixed_case_searchs-10     5.00B ± 0%     5.00B ± 0%   ~     (all equal)
GetGlob/GetGlob-10                                 0.00B          0.00B        ~     (all equal)

name                                            old allocs/op  new allocs/op  delta
GetGlob/Default_cache-10                            0.00           0.00        ~     (all equal)
GetGlob/Filenames_cache,_lowercase_searchs-10       0.00           0.00        ~     (all equal)
GetGlob/Filenames_cache,_mixed_case_searchs-10      1.00 ± 0%      1.00 ± 0%   ~     (all equal)
GetGlob/GetGlob-10
```

1 files changed, 4 insertions, 3 deletions

diff --git a/hugofs/glob.go b/hugofs/glob.go
index e691cdc10..1b649a283 100644
--- a/hugofs/glob.go
+++ b/hugofs/glob.go
@@ -26,19 +26,20 @@ import (
 // Glob walks the fs and passes all matches to the handle func.
 // The handle func can return true to signal a stop.
 func Glob(fs afero.Fs, pattern string, handle func(fi FileMetaInfo) (bool, error)) error {
-	pattern = glob.NormalizePathCaseSensitive(pattern)
+	pattern = glob.NormalizePathNoLower(pattern)
 	if pattern == "" {
 		return nil
 	}
+	root := glob.ResolveRootDir(pattern)
+	pattern = strings.ToLower(pattern)
 
-	g, err := glob.GetFilenamesGlob(pattern)
+	g, err := glob.GetGlob(pattern)
 	if err != nil {
 		return err
 	}
 
 	hasSuperAsterisk := strings.Contains(pattern, "**")
 	levels := strings.Count(pattern, "/")
-	root := glob.ResolveRootDir(pattern)
 
 	// Signals that we're done.
 	done := errors.New("done")