Refactor additional messages for new monsters spawning.

Not sure why do we need both these and "comes into view".

This includes simplification of:
* shoving the player out of stairs
* "wandering" monsters spawning on the stairs
* fancy messages for in-LOS abyss spawns

For the last part, they had really obscure probabilities, this commit makes
them easier to read.  Also, it avoid mallocs and RNG calls, but that's a
rather negligible optimization.

This commit eliminates a mysterious call to viewwindow() as well.  A comment
claimed that "Special case: must update the view for monsters created in
player LOS." yet this was not done for band members.  It appears removing
that call has no ill effects, but I might have missed something.

1 files changed, 24 insertions, 0 deletions

diff --git a/crawl-ref/source/random.cc b/crawl-ref/source/random.cc
index cd617c8b1a..ec4ebfec8c 100644
--- a/crawl-ref/source/random.cc
+++ b/crawl-ref/source/random.cc
@@ -87,6 +87,30 @@ const char* random_choose<const char*>(const char* first, ...)
     return chosen;
 }
 
+const char* random_choose_weighted(int weight, const char* first, ...)
+{
+    va_list args;
+    va_start(args, first);
+    const char* chosen = first;
+    int cweight = weight, nargs = 100;
+
+    while (nargs-- > 0)
+    {
+        const int nweight = va_arg(args, int);
+        if (!nweight)
+            break;
+
+        const char* choice = va_arg(args, const char*);
+        if (random2(cweight += nweight) < nweight)
+            chosen = choice;
+    }
+
+    va_end(args);
+    ASSERT(nargs > 0);
+
+    return chosen;
+}
+
 #ifndef UINT32_MAX
 #define UINT32_MAX ((uint32_t)(-1))
 #endif