Fix bug 92348, browser won't start if cache capacities set to 0. Added

check to fail nsCacheService::ActivateEntry() if neither disk or memory
cache devices are enabled, or if the memory cache device is not enabled
and the request if for a non-stream-based entry. r=gagan, sr=dougt.

Also changing pref name for cache parent directory according to suggestion
in bug 78480.  r=gagan, sr=darin.

netwerk/cache/src/nsCacheService.cpp

@@ -53,7 +53,7 @@
 #endif
 
 #define DISK_CACHE_ENABLE_PREF      "browser.cache.disk.enable"
-#define DISK_CACHE_DIR_PREF         "browser.cache.disk.directory"
+#define DISK_CACHE_DIR_PREF         "browser.cache.disk.parent_directory"
 #define DISK_CACHE_CAPACITY_PREF    "browser.cache.disk.capacity"
 
 #define MEMORY_CACHE_ENABLE_PREF    "browser.cache.memory.enable"
@@ -815,6 +815,9 @@ nsCacheService::ActivateEntry(nsCacheRequest * request,
     if (result) *result = nsnull;
     if ((!request) || (!result))  return NS_ERROR_NULL_POINTER;
 
+    if (!mEnableMemoryDevice && (!mEnableDiskDevice || !request->IsStreamBased() ))
+        return NS_ERROR_FAILURE;
+
 
     // search active entries (including those not bound to device)
     nsCacheEntry *entry = mActiveEntries.GetEntry(request->mKey);