Cmdline: use exceptions for control flow

This is generally frowned upon but it makes this code 10x cleaner.
We handle commandLine usage msg printing by using exceptions for
control flow. This allows us to centralize the logic for killing
the Mind threads in one place. At least with respect to printing
the usage msg.

smocore/opts.cpp

@@ -1,6 +1,7 @@
 #include <opts.h>
 #include <iostream>
 #include <stdexcept>
+#include <exception>
 #include <getopt.h>
 #include <string>
 #include <vector>
@@ -8,6 +9,28 @@
 #include <sstream>
 
 
+OptionsParserError::OptionsParserError(
+    const std::string& errorMessage, const OptionParser& parser
+)
+: std::invalid_argument(errorMessage + "\n" + parser.getUsage())
+{
+}
+
+const char* OptionsParserError::what() const noexcept
+{
+    return std::invalid_argument::what();
+}
+
+JustPrintUsageNoError::JustPrintUsageNoError(const OptionParser& parser)
+: message(parser.getUsage())
+{
+}
+
+const char* JustPrintUsageNoError::what() const noexcept
+{
+    return message.c_str();
+}
+
 struct option OptionParser::longOptions[] = {
     {"devicespec", required_argument, 0, 's'},
     {"spec", required_argument, 0, 's'},
@@ -59,9 +82,9 @@ void OptionParser::parseArguments(int argc, char *argv[], char **envp)
 
             if (stat(optarg, &info) != 0 || !(info.st_mode & S_IFDIR))
             {
-                throw std::invalid_argument(
+                throw OptionsParserError(
                     std::string(__func__) + " - The specified path is not a "
-                    "directory: " + optarg);
+                    "directory: " + optarg, *this);
             }
 
             senseApiLibPath.push_back(optarg);
@@ -71,12 +94,11 @@ void OptionParser::parseArguments(int argc, char *argv[], char **envp)
             verbose = true;
             break;
         case 'h':
-            printUsage = true;
-            return;
+            throw JustPrintUsageNoError(*this);
         case '?':
-            throw std::invalid_argument(
+            throw OptionsParserError(
                 std::string(__func__) + " - Invalid argument encountered: "
-                + std::string(argv[optind - 1]));
+                + std::string(argv[optind - 1]), *this);
         }
     }
 }