makeRe globstar should match zero+ path portions

This implements the requisite negative lookahead/behind using JavaScript
while building the regexp, so that the regexp returned by makeRe will be
able to match ** patterns against zero or more path portions, rather
than against 1 or more, which was previously a shortcoming of makeRe.

Also, move the pattern regexp tests into snapshots, where they belong.

Fix: isaacs#157

minimatch.js

@@ -791,13 +791,42 @@ class Minimatch {
       : twoStarNoDot
     const flags = options.nocase ? 'i' : ''
 
-    let re = set.map(pattern =>
-      pattern.map(p =>
-        (p === GLOBSTAR) ? twoStar
-        : (typeof p === 'string') ? regExpEscape(p)
+    // coalesce globstars and regexpify non-globstar patterns
+    // if it's the only item, then we just do one twoStar
+    // if it's the first, and there are more, prepend (\/|twoStar\/)? to next
+    // if it's the last, append (\/twoStar|) to previous
+    // if it's in the middle, append (\/|\/twoStar\/) to previous
+    // then filter out GLOBSTAR symbols
+    let re = set.map(pattern => {
+      pattern = pattern.map(p =>
+        typeof p === 'string' ? regExpEscape(p)
+        : p === GLOBSTAR ? GLOBSTAR
         : p._src
-      ).join('\\\/')
-    ).join('|')
+      ).reduce((set, p) => {
+        if (!(set[set.length - 1] === GLOBSTAR && p === GLOBSTAR)) {
+          set.push(p)
+        }
+        return set
+      }, [])
+      pattern.forEach((p, i) => {
+        if (p !== GLOBSTAR || pattern[i-1] === GLOBSTAR) {
+          return
+        }
+        if (i === 0) {
+          if (pattern.length > 1) {
+            pattern[i+1] = '(?:\\\/|' + twoStar + '\\\/)?' + pattern[i+1]
+          } else {
+            pattern[i] = twoStar
+          }
+        } else if (i === pattern.length - 1) {
+          pattern[i-1] += '(?:\\\/|' + twoStar + ')?'
+        } else {
+          pattern[i-1] += '(?:\\\/|\\\/' + twoStar + '\\\/)' + pattern[i+1]
+          pattern[i+1] = GLOBSTAR
+        }
+      })
+      return pattern.filter(p => p !== GLOBSTAR).join('/')
+    }).join('|')
 
     // must match entire pattern
     // ending in a * or ** will make it less strict.

package.json

@@ -10,6 +10,7 @@
   "main": "minimatch.js",
   "scripts": {
     "test": "tap",
+    "snap": "tap",
     "preversion": "npm test",
     "postversion": "npm publish",
     "prepublishOnly": "git push origin --follow-tags"