Merge 10.6 into 10.10

The MDEV-29693 conflict resolution is from Monty, as well as is
a bug fix where ANALYZE TABLE wrongly built histograms for
single-column PRIMARY KEY.
Also includes a fix for safe_malloc error reporting.

Other things:
- Copied main.log_slow from 10.4 to avoid mtr issue

Disabled test:
- spider/bugfix.mdev_27239 because we started to get
  +Error	1429 Unable to connect to foreign data source: localhost
  -Error	1158 Got an error reading communication packets
- main.delayed
  - Bug#54332 Deadlock with two connections doing LOCK TABLE+INSERT DELAYED
    This part is disabled for now as it fails randomly with different
    warnings/errors (no corruption).

sql/sql_error.h

@@ -29,6 +29,14 @@ class THD;
 class my_decimal;
 class sp_condition_value;
 
+/* Types of LOG warnings, used by note_verbosity */
+
+#define NOTE_VERBOSITY_NORMAL             (1U << 0)
+/* Show warnings about keys parts that cannot be used */
+#define NOTE_VERBOSITY_UNUSABLE_KEYS      (1U << 1)
+/* Show warnings in explain for key parts that cannot be used */
+#define NOTE_VERBOSITY_EXPLAIN            (1U << 2)
+
 ///////////////////////////////////////////////////////////////////////////
 
 class Sql_state
@@ -1073,6 +1081,11 @@ public:
     return m_statement_warn_count;
   }
 
+  uint unsafe_statement_warn_count() const
+  {
+    return m_statement_warn_count;
+  }
+
   /**
     Get the current errno, state and id of the user defined condition
     and return them as Sql_condition_identity.